I concur, the GeForce 7900 GT kicks both their asses.
The Radeon 1900 XT/XTX is quite a jump from the 7800 GT, but NOT that much of a jump from the 7800 GTX. In fact the GeForce 7900 GTX (vs GT above) will typically outperform the Radeon 1900 XT in 'one on one' tests, even with high FSAA.
Since ATIs former strength over nVidia was FSAA, and they no longer hold that advantage, and that GeForce 7900 GTX with 1.8 GHz x 256 bit GDDR3 are available, the Radeon 1900 XTX has now been..... left behind.
The 7900 'GT' is the slightly weaker brother of the 7900 'GTX'
Check the XFX website for higher clocked 7900 'GT' cards btw, you might be able to gain another +20% on top of the two cards you're looking at... for the same price. 8)
I dislike the Radeon 1800 XL/XT GPU because: It only has one quarter (1/4) the shading pipes when compared to the Radeon 1900 XT/XTX. This hurts its performance significantly in some titles. Then bear in mind the 'above' suggestions can outperform it.
My last 6 video cards have been ATI GPU based ones aswell... but the tides just turned in late March '06. I am seeking a GeForce 7900 GTX (XFX varient with the 1.8 GHz GDDR3) btw.