Should be ok, but if you have doubts there are the 2GB HD69x0 cards. I would go with the 570 SLI setup as a personal preference as I experienced various issues with AMD cards when using a dual-link DVI output at 2560x resolutions.
The best value is the 6950, they have 2 gig frame buffers and will overclock to preform like the 6970. You can get a pair of 6950 for $540.00 or (334.68 GBP)