GeForce

The Ultra is faster, but you shouldn't buy one unless you have millions of dollars. If the price of the ultra is even 0.1% of your current cash holdings, get the GT instead. The performance difference is practically negligable while the price difference is insane.

I *think* the GT is the better of the 2, but I'm not entirely sure (....or not). You should be able to get details to compare them by on the nVidia site. Also, if you're getting a new motherboard, get one which supports PCI-Express. AGPx8 is *soooooo* yesterday :)

GT is an underclocked Ultra. I say get the GT, requires one molex AFAIK so no 480 PSU and it takes up one slot. If you want the Ultra good luck finding one as both ATi and NVIDIA have been having problems with their high end cards.

6800 Ultra isn't too hard to find, unless you want the PCI-E version. AGP versions are easy enough.

As has been said, the Ultra is fastest, but the difference is only in clockspeed. Since they have the same number of pipelines and shader units and everything else, the performance difference isn't that big.

The Ultra works with only one molex plugged in as well, although for stability, using both is a good idea. And it doesn't need 480W, unless you're a hardcore overclocker, and have a ton of other power-hungry hardware in your system.

I too will recommend the 6800 GT, owning an XFX one myself. As mentioned, it is essentially an underclocked Ultra and many people have flashed it and OC'ed it to ultra levels. The slight performance gain is not really worth the money difference between the cards. And yes, it requires only one molex