GeForce GTX 580 vs. Radeon HD 5970 2GB Performance
 

The HD 5970 delivers faster gaming framerates compared to the GeForce GT 580. However, if you look at the actual usability of those frame the picture is a bit different. The GeForce GTX 580 allows a consistently higher level of the gameplay experience compared to the Radeon HD 5970. We were able to game at higher settings with the GTX 580 than we were with the Radeon HD 5970. The most important factor, beyond framerates, is the visual quality and experience returned by the product. The GeForce GTX 580 allows a more immersive, smoother, and consistent quality of gameplay.

http://www.hardocp.com/article/2010/...b_performance/