Having similar problems. Been playing BF3 for a while with no framerate issues. I installed Arma 2/DayZ mod 2 days ago and now most of my games run at severely low FPS. Hell, even my Diablo 2 is acting funny.
Night time in server, started up, proned into a house. Nothing coming at me. FL not on. I go to pick up a crowbar (Im not moving at all) Zed attacks through wall of the building. sigh