The final speeds won't be known until the middle of April, but ATI can get the R600 to work at a quite high 750 to 800 MHz. We are talking about the core speed here.
We already said that GDDR3 has priority, and we again confirmed that there won't be any 65 nanometre R600 part.
The new / old R600 still needs a new driver to get it works better, but from what we hear it still needs a lot of tweaking. The official launch is still scheduled for May and late April might be the date for an NDA presentation.