to quote toms hardware in their long ass article,
Conclusions
With price tags of $550 and $725 respectively, the Geforce 8800 GTX and Ultra are anything but cheap. That's a lot of money to invest into 3D gaming. Under DirectX 10, these graphics processors really fly. While their performance lead over the Radeon 2900 XT and the Geforce 8800 GTS was not as pronounced under Windows XP/DirectX 9, they offer between 50 and 100 percent more performance than these cards under Vista/DirectX 10. Additionally, the Geforce 8800 Ultra boasts much shorter load times in Lost Planet and Bioshock. We can only guess how well the GTX and Ultra will be able to handle upcoming titles such as Hellgate London or Crysis. However, these cards pack a major punch and still have some performance reserves.
Today, the Geforce 8800 GTS and the Radeon HD 2900 XT constitute the new mid-range. They offer sufficient frame rates for a smooth game experience in current titles, although FSAA may need to be disabled in higher resolutions. Of these cards, the Geforce 8800 GTS 320 has a minor advantage in performance and a major one regarding its pricing. The pricing of the Geforce 8800 GTS with 640 MB positions it directly against the Radeon HD 2900 XT. Don't forget to factor in the much louder reference cooler of the Radeon card, though - Nvidia's solution is much quieter.
In the lower performance segment, the Geforce 8600 currently looks like the better choice than the Radeon 2600. Specifically, we would recommend the 8600 GT, which can be found for as little as $120 as a standard version and $130 as an OC variant. Alternatively, you could also go with a Radeon HD 2600 XT with 256 MB.
The Geforce 8400 GS, 8500 GT and Radeon HD 2400 all run DirectX 10 game flawlessly. However, you will have to do without FSAA and set the graphics quality slider no higher than the medium setting to achieve playable frame rates.
For now the 8800GT is the clear cut winner but later on, maybe ati might throw up a bomb or two.