So this is an engine bug that affects only a small range of users: those with very heavy modlists + a high refresh rate monitor. Basically if you have a really heavy modlist, the game's performance gradually nosedives over an hour or so as you play. I believe the reason this happens is that the engine cannot handle loading and unloading so many high res NPCs and textures and models. It's probably not that noticeable for people who play at 60 FPS but I have a 120hz monitor and the performance degradation is extremely noticeable even after only 30 minutes. When I initially load in to a random stretch of road outside Goodsprings, I have 120 FPS. After 30 minutes it's down to 100 FPS in the same area. After an hour it's about 80 FPS. Approaching hour 2 it's now down to 60 FPS. This is the point where I am forced to restart the game because the low framerate is making me feel sick.

The bug still occurs with every optimization mod installed including making the executable LAA.

I'm not sure where to post this but I want to raise awareness of it. I've recently had a discussion with someone else who has the same issue (he had 700 mods, I'm running 400). I've also seen it discussed on the Steam forums. If any of you NVSE coder wizards are reading this I would really appreciate if you could take at look at what's happening. I would happily bugtest any fixes for this seeing as it's probably not a bug that the average player has.