R600, DDR3 card probably called Radeon X2900 series will come with the memory working at a modest 1600 MHz. Don’t forget that R600 has a 512 bit memory controller and that it will have some impressive bandwidth.
GDDR4 version comes later and should have a clock even higher than 2000 MHz milestone. We already told you that ATI can clock R600 at 750 to 800 MHz.
R600 is of course an 80 nanometre chip and production should start in April time with some availability and launch scheduled for May.