Here are the results of the comparison against the GeForce 8800 GT 512MB. In these two tests the performance difference is very small. For people who play at 1280 x 1024 pixels this is a pretty interesting card.
Check out the site for more results, they also compared the card against the Radeon HD 3850 256MB and the GeForce 8600 GTS 256MB. The 8800 GT 256MB is much faster than the GeForce 8600 GTS 256MB and in most of the tests the card was also significantly faster than the Radeon HD 3850.