I run a AMD 940 BE (AM2+ I think) quad and I do not have the problems, but also I run XP pro. Some times I do get frame rates drops, not real bad ( 30 sometimes). I also run AV and many other processes in the background.. 62, 63 processes in that area.
I also do not run the optimizer. I bought my 940 from newegg as a open box at the time, it was from 90 to 100.
Also I use 3 year old xfx 8800 gt, kingston hyperx t1 4 gig RAM.