only get the 640 version if you plan on playing games above 1600x. i have a evga 8800gts 320 running @ 667/1051 and i play bf2 at 1600x1200 max everything(aa&af) and my fps dont drop below 80, average is around 150.
e4300@3420mgh(380x9)
ga 965p ds3 re
2gig g.skill 6400h @ 950 4-4-4-10