ACOK is a great mod, I (used to) prefer it over A World of Ice and Fire. But a major flaw in ACOK is the large sizes of textures in many hard-to-notice things like small rocks and trees. I've reduced the textures of those things to about half of what they originally were, I also did the same to many building, weapon and armour textures as well. As I tested them in the mod, it looks very much the same but I had a noticeable FPS boost. People can reduce these textures on their own but it can be tedious and time consuming.

• How to Install
  

• Download the rar/zip and open it when it completes.
• Drag the folder into your modules/ACOK.
• It should ask to replace the files, say Yes. (I also recommend to create a backup of your ACOK/textures folder in case you don't like the FPS boost)
• And you're done! Run the game as you normally do.