I think they're all very good cards, but I personally like the X800 XT's
the 6800 performs better in most cases, except when the settings for games are all up high, and using these cards you'd want the settings to be up high anyway
Remember the the X800 does not support pixel shader 3.0 there will be a noticeable big differnce compared to the 6800. Of course the x800 will still run excellent as it is the best for its brand but the 6800 does have an edge. Far cry is one of the new games that uses pixel shader. http://www.firingsquad.com/hardware/far_cry_sm30/page3.asp
okay what is this pixel shader... I have heard it all over the place when trying to compair these two videocards. Nvidia 6800 has it i know this. And does it really make that big of a diff... I know the ATI has a better clock speed... hmmm... lets have a look at that link flash_aaa put up there...
The graphics will be wicked with Pixel Shader 3.0. Just compare FarCry screenshots with and without it enabled. Its amazing! The ATI X800 scores better in the benchmarks however. What it comes down to is what do you want? Do you want faster framerate or better quality. ATI cards offer faster framerate at the expense of some image quality. NVidia cards offer better image quality including PS3.0. With so much more to render, its logical that the framerate of an nvidia card would not be as high as its ATI opponents.