X1900XTX VS 7900GTX:
http://www.xbitlabs.com/articles/video/display/gigabyte-1900-7900.html
To cut the long story short, Gigabyte Radeon X1900 XTX and Gigabyte GeForce 7900 GTX have their advantages and drawbacks and it all depends on the game. The performance of Gigabyte’s both flagship solutions is quite high for gaming with enabled full-screen antialiasing, however if we look at them from the long-term prospective, then the ATI R580 model will be preferable, because the shader effects with complex mathematical calculations is going to grow bigger with the time.
As for the peculiarities of these two particular graphics solutions, there are not too many of them worth mentioning here. I would certainly like to point out great packaging design and free games included with the cards. And although Gigabyte GeForce 7900 GTX comes bundled with only one free game, the quality of the game makes up for the single title included. I have the feeling that they could have made a bit richer bundle for the high-end cards like that, but if you do not really care about the availability of free software, then either of these cards may become a great choice for you
X1950XTX VS X1900XTX VS 7900GTX:
ATI’s new Radeon X1950 XTX is a worthy successor to the Radeon X1900 XTX, the previous flagship product in the R580-based series. Equipped with new-type memory, capable of working at an unprecedented frequency of 1000 (2000) MHz, the card has got faster and better than the GeForce 7900 GTX where the Radeon X1900 XTX used to lag behind. As might have been expected, the biggest performance growth is observed when full-screen antialiasing is used along with high resolutions. The value of this growth varies from 5% to 20%, but is zero in some cases, e.g. in Call of Duty 2, F.E.A.R., and Tomb Raider: Legend. Anyway, this is an excellent achievement considering that the new card’s specs differ from the older model’s in only one point.
We also want to single out the fact that having the same or higher performance than the GeForce 7900 GTX, the Radeon X1950 XTX provides a much higher quality of anisotropic filtering. This is not too conspicuous in the heat of a battle, but the difference is striking in some cases. The Radeon X1950 XTX is undoubtedly preferable in this respect. Besides that, like any other member of the Radeon X1000 family, the new card from ATI permits to use FSAA and enhanced floating-point color representation (HDR FP) simultaneously which greatly improves the visuals in some games, e.g. in TES IV: Oblivion. Having two G71 chips under the hood, the Nvidia GeForce 7950 GX2 cannot offer anything like that with regards to image quality, but is ahead of the Radeon X1950 XTX in performance across a number of applications.