This mod focuses on 3 main things.
Increasing FPS where possible, lowering the amount of network traffic being sent between clients and server, and reducing checks and actions being made that consume CPU.
This mod also addresses a few game bugs as well.

Please note that there is only so much that can be done via XML over changing actual game code. This is a large bandaid but it is not a cure.

Additions are ongoing as more sources of CPU usage, netcode and client FPS lag are found and methods of squashing them are discovered.

*NOTICE*
DO NOT INSTALL THIS MIDWIPE/SAVE.
This mod adds items and changes quests, which will corrupt existing savegames!

Please read the README file in the mod to see the full list of changes.

There are two potentially controversial/large changes that not all players will want, examples being;

Trees and Cacti no longer decorate outside of view distance limit.
This stops a bug where the distant decoration feature of trees does not update to all players despite a tree being cut down. Example: Player A cuts down tree. Player B has not been in Player A's chunk yet, but sees the distant decoration version of the tree that has been cut down. Player B walks into player A's chunk, and the tree respawns with one health. This respawned tree will also destroy anything in its path of regrowth, including bases.
Unfortunately, this will lead to the jarring effect of trees and cacti "popping in" as you move around the world, and is detrimental to immersion.
(To delete this part of the mod, delete the blocks.xml in the zzz_performance folder.)

All resource based items have been given a second alternative recipe that allows crafting them in bulk.
This does not remove or change the existing recipes. It instead adds an option under the original that allows the player to craft said item in bulk instead. The goal being to lower frequency of items being crafted. Every time a single item crafts while the player remains in the workstation's UI, it fires a NetPackage, which adds up quickly. The bulk crafting gives players a 20% material discount to persuade them to make bulk stacks instead of singles, thus spreading out crafting greatly and reducing net traffic.
This may have a detrimental effect on server balancing as not everyone will want this due to making crafting cost slightly less.
(To delete this part of the mod, delete the items.xml and recipes.xml in the aaa_performance folder.)

While specifically aimed at high population multiplayer servers, there is no reason this won't work on lower population ones. It is simply there to help with the worst and will no doubt help with any server size.

UPDATED 7/4/2023
V5 Release.
-A21 Compatible
-Fully compatible with any other mods.
-Commented out window replacements due to a21 fixing frame drops with them.
-Removed Empty Can and Jar Bundles
-Made simpler to disable distant trees and cacti.