His res is 1920x1200 and his current card is a GTX 295.
I said that he wouldn't see much of an improvement because his CPU would be holding the 580 back so much, its probably even holding his 295 back. tbh, the 580 performs well at 1920x1200 so I would have thought that the bottleneck would still be quick high, even higher for the fact that the CPU would be struggling even more.
Out of interest, if he oc'ed would he still see a bottleneck?