We have informed you that R600 XTX will get delayed till some unknown future but we also learned that R600XT will cost acceptable $ / €399. You can read more here.
You can hold your breath as you won't be able to buy this card at least till middle of the May but we heard that it should compare well versus Geforce 8800 GTX. The only trouble is that Nvidia is working on G80 Ultra and no one really knows how god that product really is.
If we had to predict the future we would say that Nvidia can easily drop its Geforce 8800 GTX price to match Radeon HD 2900 XT price and the performance should be close anyway.
R600XTX is scheduled for a later announcement, no one really knows when but the first 1024 MB cards might get finalized only in late May so you can assume that you might see some of these cards at Computex in early June.