As far as x1950xtx vs. G80:
anandtech obilivion benchmark
I would say the 8800gts 320mb version will be slightly better then the x1950xtx considering how well the 8800gts 640mb version holds up against the x1950xtx. But it is dx10 ready, so you will have a little more future proof. But a lot of ppl still say its too early to go dx10 since....well there won't be too many dx10 games coming out for a while ( i know supreme commander will support dx10).
So in the end its your call. Get the dx10 card now and don't have to get one later (like probably a year till dx10 starts to look really nice with newer games), or get the x1950xtx and probably end up selling it later for a dx10 card at the most a year from now (im just guessing but that seems about right considering technology and newer games and well you know....the technology world....you can't seem to keep up with it