Same problem, damn FPS drops in random areas. The game ran smooth in P2~P3. Same rig on P4~EA and FPS drops as hell randomly.

Intel i5 2500 @3.3Ghz
GTX 680 Zogis
8GB Ram Corsair
Windows 7 Ultimate

165~185 FPS that dramatically drops to around 35 FPS facing certain directions even without any player activity.