I get big framerate drops and lags/stuttering in places with mist and fog, especially in the swamp areas around solitude. Even more so when the area is bigger. Any tips on how to improve performance as in any adjustments to be done in the game options?

Otherwise my game runs on Ultra settings (except shadows being on med) and I get a 40-50 FPS outdoors and 60+ FPS indoors (except in caves with a lot of particle effects which takes it to 30 FPS).