I didn't try to measure performance in this game, but it was interesting to compare the qualities, especially considering the amount of complaints about the way various cards work in this application. As we see, the rivals showed identical qualities with no artefacts.
QUALITY ISSUES
GeForce 6800 Ultra
RADEON X800 XT
Vietcong
The results are simlar to the previous ones: no difference between R420 and NV40.
QUALITY ISSUES
GeForce 6800 Ultra
RADEON X800 XT
3DMark03 - Game1
The lightest mode (no AA or anisotropy): NV40 wins.
The heaviest mode (both AA and anisotropy): NV40 loses with 400 MHz and equalises with the help of 450 MHz.
Thus:
NVIDIA GeForce 6800 Ultra 450MHz vs. ATI RADEON X800 XT: roughly, a parity.