i really can't be bothered to explain, but click here to get al the info on this range. At last ATI have done a very fine job. personally i'm with geforce on the basis that most games are designed for the nVidia
The GeForce 6800 series. Both the 6800 and 6800 GT owns the X800 Pro. The X800xt owns the 6800 Ultra by like 5-10 fps (which is hardly a noticeable difference if you are actually having fun). Plus the X800 Series uses Pixel Shaders 2.0 and 6800 uses 3.0, meaning that the 6800 might last longer for future games using 3.0.
In perfomance and also quality, they are both equal.
In technology, the 6800 "should" have the upper hand.
Well, personally I think ATi has barely won this round....
Performance wise they are about the same, both taking their fair share of wins and loses.
But obviously you have to also note the power supply demands(the X800XT uses less power then the 9800XT) and the fact that the Nvidia stills has a massive heatsink/fan combo that takes up the advacent PCI slot.... That I think gives ATi the edge, but both are great fine cards