Originally Posted by Madpistol
The GTX 570 is the faster card. The 2GB of framebuffer on the 6950 will serve you better on future games, though.
Unless Madpistol is a software developer working on a game that will require more than 1.28GB of VRAM at the OPs native res, I don't know how he (or anyone) can make this prediction.
The fact of the matter is most games are console ports, and consoles don't have 2GB of VRAM. The VRAM issue is only in play if the OP is thinking about going to three monitors, which hasn't been stated here.
For the hardware he has, the GTX570 is the better choice. Unlocking a 6950 isn't guaranteed, and has destroyed cards.
As far as the reputed "5fps difference" goes: