Radeon HD 2900 XTX still didn't get its face. That's why AMD told everyone that they will go for a unified product launch, so the R600 XT part only. TBD part always means to be discussed and you can see it often in a future plans.
The big European resellers got a word that there won't be any Radeon HD 2900 XTX part anytime soon. The launch involves Radeon HD 2900 XT as the high end part at €434 price tag that might sunk down to €399 at final launch.
It is still unknown when the GDDR 4 XTX version comes out and if it comes out at all. I guess that this depends of how good is R600XT and how good is Geforce 8800 Ultra.