DailyTech had some time with the two cards and was able to benchmark them against a Geforce 8800GTX. The 2900XTX is really fast but is nothing compared to the 8800GTX, although the 2900XT is faster than the 8800GTS.
Seems like both sections of AMD are having some problems graphics cards and CPU’s.
In Elder Scrolls IV: Oblivion:
Radeon HD 2900XTX got 75.1 FPS
Radeon HD 2900XT got 73.4 FPS
Geforce 8800GTX got 98.4 FPS
all of the other data looks very similar but I would suggest checking it out.