ok heres the deal:
There will be two versions of the XT available.

1st: 2900 XT 512mb gddr3 743/828 default clks
2nd: 2900 XT 1gb gddr4 749/1009 default clks

For the price difference of 1gb version not really worth it as
the gddr3 version can hit 1000mhz on mem. anyways.....