it can be a problem with the game aswell. as i said, a few weeks ago, before patch 2.5 went live, i had no issues at all. now the performance is down and my system hasnt changed a bit in the last few weeks..
32 bit, fore-background is set up, vsync is off.
before 2.5 i had stable 110fps, now its somewhere in the range of 60-90
+ some more performance issues and heavy fps drops (below 3fps) when i enter a new game and sometimes a new area... performance wise 2.5 has been a total disaster for me.