The 6950 and 560 are very closely tied in terms of value. They will both perform roughly the same and are priced very closely with each other. I would edge towards the 6950 in your case as the 6950's extra memory would be better suited to that type of resolution.
Btw, regarding the chart on that site, its only a synthetic benchmark, not real world performance, so don't take much from it.
All right but one question. What you mean by, "synthetic benchmark". Please elaborate, I'm a "youngster".