+++ please refer to my user profile about me page and follow my recommendations how to use my mods as an addition to nexusmods terms +++

added jan 2024:
1. be aware that the boston AIO was not updated since 2019 (see under essential advices 1.). if you face incompatibilies with recent mods changing previs data check option 2.! Load order is very important!
2 another newer mod is (PRP) trying to solve vis conflicts while optimizing fps. it gets recent uptates and patches. try this instead as an option.

I personally still use boston aio without problems so far. please contact prp mod author in case of mod related questions. thank you!

this mod is intended to be game performance tutorial and a ctd and stutter knowledge base for people who encounter ctd or fps drops in dense areas like mass fusion center, settlements with many objects or goodneighbour. take 3 minutes of your time to read this page. with this knowledge you will never have to wonder again while you encounter sudden fps drops in some areas! you will find the background and solutions for that problem here!
if you follow my advices i guarantee you that you will get the best possible performance for your game. all recommendations, correctly applied, are tested and confirmed by many users! if you have suggestions or complains let me know.

background: fo4 uses a new feature not used in skyrim or skyrim se - previs/precombines.
this is no brand new information but it means that you cannot handle fo4 like skyrim regarding modding. fo4 optimizes performance but it makes things also more complicated for modders and gamers. so read carefully!
if you ignore this while adding mods or using mods or disable vital features in your ini you should be aware to run into performance problems, graphical glitches or even ctd sooner or later.

for dx11 an obvious limit is about 11000 to 12000 draw calls (fo4 and skyrim se). only one (virtual) cpu core is used to address vital draw call data to the gpu. you can monitor how the fps drop above this dc value due to the cpu to gpu engine bottleneck, regardless how strong your gpu is. in regions of 15000 draw calls you already lost 20% of your fps or even more while one cpu core has to do the important work while gpu has to wait and in extreme case idles. only a very high single core ipc can cure this to some extent.

read more about dx12 and the difference to older limited interfaces also used for fallout 4 and you find the reason why nvidia rendering often performs better than intel and amd with older games.


so be aware of the practical draw call limit for dx9 and dx11 interface depending on the game you play and you would like to mod. nividia drivers seem to perform slightly better due to better optimized drivers than amd:
for dx9 limit is about 6000-10000 (oblivion and oldrim), depending on the game engine and hw (uses only one cpu  thread!).
for dx11 it is about 11000 to 12000 (fo4 and skyrim se) depending on the game engine and hw (uses only one cpu  thread!).
and dx12/vulkan are able to handle 200000 and even much more draw calls (uses multiple cpu threads!) but only new games support this interface.

essential advices to reduce performance and fps drops:

1. use BOSTON AIO FPS fix mod . prp mod pack exists exists as an allternative solution as far as i know. i recommend to reduce any not essential scrap activities outside settlement boundarys to zero until you know what you can permanently destroy! read the mod description carefully! if you do not play fo4 with extreme visual changes in the exterior this mod will definitely help in dense areas inculding the dlc's!

2. use a dynamic shadow and load accelerator like this one (tested and working fine!). badly adjusted shadow settings are performance killer No1. together with god rays and extreme ambient occlusion settings (looking ugly and artificial by the way)

3. Do not use any sort of scrap mods for any sorts of static objects if you do not need to (see also 1.) and if you are not sure if this hurts the vis/precombines fo4 performance optimization and stabilty. Try to mod by adding objects instead of changing or deleting existing ones! do not add too much additional clutter in one (already dense) area! the more added clutter the higher the risk of fps drops!

4a. check mods changing objects, for taking care not to destroy previs/precombines optimization! all sorts of trash cleaning mods are suspicios and
often they do harm to performance. avoid mods changing bigger objects in dense areas without delivering updated vis/precombine data. only a few mods include a warning or deliver needed vis/precombine updates. if a mod urges you to change ini setting to  bUseCombinedObjects=0 it is probably a sign that vis/previs are not generated correctly. 

4b. check also mods adding or capable adding high amounts of clutter, some even automated by script like sim settlements to work within the fo4  object limits! if you are not aware they slow down your game, produce ctd or can ruin your save.

5. you can try to solve some draw call related problems if the hardware is compatible and seems badly optimized.
try my cpu core optimization method for cpu supporting smt/hyperthreading. it works for many games.
a vulcan api wrapper called DXVK may work for you. watch my sticky post and crosscheck my sse fps droptutorial for updates on that! it is beta and does not run with all hardware or game settings!


if you like to play fo4 with ugristoload=7 with stable fps these 5 steps are even more important!

check if use of previs/precombines is activated (default setting). it reduces draw call amount in dense areas to a maximum of about 12000
(vanilla). about 12000 draw calls is the limit for dx11 before stutter and sudden fps drop occurs. very high numbers will end up even in ctd.
you can check that with installed enb (see next paragraph).
check Fallout ini files for  bUseCombinedObjects=1 and bUsePreCreatedSCOL=1 (activated)
check if ugridstoload=5 (max. 7 for strong hw, higher ugrids means larger full detailed objects grid) are loaded. this raises the amount of draw calls and the risk of values beyond dx11 limitation. i play with ugrids=7 but this is at the limits for the engine and stable gameplay in dense areas and you should own strong hardware! ugrid values beyond 7 are possible (maybe for screenshots and tests) but nonsense and a major stability risk for gameplay.

check also for your fov setting. fov above 80 means more objects and more draw calls in a scene and may also reduce fps in dense areas and raise draw calls. you can try that by changing fov in these areas (set fov=xx). lower fov means lesser bottleneck and higher fps.

check if you have mods installed which install many objects in the exterior (without providing generated previs/precombines).
check for mods destroying precombines (happens often unintentionally or due to lazyness).
too many mods disabling precombines will raise draw calls too much and hurt performance!
see also my sticky post for recommendations and updates!

essential ini settings to heal or avoid blurry textures loaded with obviously too low resolution
it is important to know that changing these settings may have a performance impact depending on your hardware especially vram the more high res textures are installed! i recommend to monitor the vram use!

fallout.ini:
[General]
bForceUpdateDiffuseOnly=0
iTextureUpgradeDistance1=7500
iTextureUpgradeDistance0=5000
iTextureDegradeDistance1=7500
iTextureDegradeDistance0=5000
fUpdateTextureTime=1.0000
bAllowTextureFallback=0
bEnableFileCaching=0  (helped me to get rid of blurry, half loaded textures)


how to check number of draw calls
if you encounter ctd, stutter or sudden fps drops in dense areas i recommend to check draw call amount with enb (or with reshade in the statistics tab) . click the profiler tab in the activated enb window and you will see a line showing you the current draw calls. this value changes if you move the camera /view. if you encounter values above 12000, sudden frame drops or stutter in areas with high amount of objects are likely to occur. check your setup or mods or the amount of objects. reason may be too complex or cluttered settlements, destroyed precombines or higher ugridstoload with the effect of producing too many draw calls in a specific area, raising over the critical limit of 15000. a risk many users are not aware of because it
is a slowly and mainly hidden growing problem in an open world game.

i recommend to fast travel to "fallen skybridge". go into the direction to goodneighbor and look down to goodneighbor.  this is known as a "very high draw call area" and a good testing area for your game setup and graphics performance.

be aware of any mod changing precombine or previs related settings. good examples are most scrap mods allowing to change static objects especially outside settlement limits. use them only with caution and if you know what you do. if you allow to destroy precombines by scrapping parts of it this may hurt performance even on a high end rig due to the dx11 draw call limitation! a destroyed precombine can raise the amount of draw calls from 1 to 1000 or more for one destoyed precombine object. the result will be a permanent nice fps drop in that area. you can check differences by comparing  a new game without mods and default settings with a gamesave containing scrapped object areas. 

an impressive example of the fps drop effect is eli's commonly used armor compendium mod close to diamond city. if you do not apply this fix you run into fps drops around eli's shop. two or three of these mods in one area and you will encounter not only stutter but ctd.

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to solve some general fallout 4 (works also with sse) texture loading problems and to see all details of you textures:
(don't use this if you you prefer high fps instead of high quality texture display also if you suffer from lower ram and vram or a weak pc don't use these settings! you will probably destroy fps!)


if you encounter general problems with blurry or not fully loaded textures (including rubble) you may try these ini-settings with sufficient vram 
READ THIS AND APPLY THE SETTINGS offered in the description.

important additional experience info regarding vram, stutter and blurry textures:
vram monitoring shows a direct relation between big sized hd texture packs and the related bottleneck you run into depending on your avalable vram.


if the loaded texures will not fit in the vram different things may happen:
1. textures begin to pop in,
2. mipmaps are not fully loaded (blurry textures) regardless of your setup.
3. and in worst case game ctd if the available ram+vram is too slow or too small to load the demanded texture files.

the only thing to prevent these scenarios:
always monitior your vram usage in demanding exterior areas! if vram is fully ulilized or already exceeds the cards nominal vram size try to reduce
the size of the loaded textures by:
1. checking for big ultra HD textures packs you do not really need or use them with reduced size! use 4k textures only for selected objects where you need them - not in a big overhaul pack unless your rig can offer huge amounts ov vram.
2. reducing the amount of mods cluttering the exterior areas with additional objects and textures !
3. buying a grahics card with plenty of fast vram (a 3090 or 3090ti card should be a safe bet) and use always a vram corresponding game (ini) setup

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if you encounter any other performance or ctd problem check stability of your hardware first because dense areas in fo4 are taxing for gpu, ram and cpu. a stable system is a requirement for tests and ctd free game. if you push cpu, gpu or especially memory settings too far you may run benchmarks but you may also ctd with fo4 randomly. fo4 is very picky regarding stable hardware.


to reduce frame drops in case your hw is capable you can try to reduce this setting slightly (add to your ini).
it will reduce the timeslice for scripts a little and gives more time for rendering (it helped me but it depends on your cpu ipc ). be cautious
and do a test! it will give you slightly more consistent fps, a few more fps and a slightly faster fps recovery in case of a frame drop.
consider a cpu with high single core ipc to compensate the reduction!

a special souce of sudden stutter and extreme fps drop scan be a conflict  with smoke effects especially combined with foggy interiors. 
to eliminate that i use the fog remover mod - smoke only esp/esl option. works like a charm in these cases.
i personally can recommend fog remover mod. it reduces load and if you like a clear look it will be a mod for you.
there is also a glitch with newer nvidia cards since touring/rtx, responsible for an instant ctd. 
if you upgrade to such cards be aware to disable this feature.


if you have other related stutter problem you probably encounter the limits of dx11 fo4 draw call interface between cpu and gpu - even with high end hardware. this draw call bottleneck between cpu and gpu exists because up to dx11 this interface is not supported by multithreading. so one cpu thread - regardless of cpu cores - has to do deliver the draw calls for all objects to the gpu.the dx11 limit is around 12000.
i tested the amount of draw calls with deactivated precombines and urgridstoload=7 in the goodneigbor area and reached up to 30000 draw calls and ended up with ctd. even an 8/16 core cpu and nvidia 2080ti showed a sudden frame drop and stutter from 55 down to 18 fps with 4k res and ultra settings without any countermeasures(see essential advices).

this background also makes the nexusmods "mod collections" effort at least questionable for open world games like fo4 and skyrim with limited graphics interface. It does not fit perfectly to games like fo4 and skyrim already suffering from some performance problems and the permanent risk of frame drops while already optimized to the limits. be sure to test mod collections performance on your rig as a help and check for any limitations.

thank you for reading. i hope this info helps to optimize your setup and to avoid common performance traps.