
Today they discovered that ATI's X1800 XT will probably feature a 625MHz core and 1500MHz memory. They also claim the memory should easily be overclocked to 1600MHz as the memory chips ATI uses are rated for this clockspeed.
It's not sure whether the GeForce 7800GTX or the Radeon X1800XT will be the fastest but it will only be by a very small margin.