At least a few partners confirmed that they will be introduce overclocked versions of the R600XT card. These cards will come some two weeks after the initial launch and most of them will work at significantly higher clocks.
The reference card works at 745 MHz core and 1656 MHz memory. There is still no confirmation if any of these cards will use a water cooler, but we wouldn't be surprised if they did.
With a reference cooler the card works stable at 840 MHz as we proved here and with a better cooler such as a few partners have in their labs, you should be able to do even more. With water we think that even 900 MHz or above should be possible.
We will try to get some clocks, but at this point we can confirm that the overclocked HD 2900 XT cards are on their way.