Caporegime
Don't bother upgrading from an 8800GTS 320 to the x38x0 series. The ATI cards are faster, but not noticeably. The same applies for 8800GT > GTS 320.
I speak from experience.
I've gone from 8800GTS 640, 2900XT to an 8800GT and the 8800GT is much faster than the GTS 640 apart from 16xAA in TDU and Dirt...