Just a small reminder because some people seem not to know:
The R500 "is" the R400, which was cancelled early this year. There are many reasons to this, among which the fact that ATI didn't feel they could deliver the R400 in the required timeframe, which is Q1 2004 ( it seems the August 2003 timeframe was either BS, or that it had already been delayed a bit before getting cancelled. )
The R500, thus made by the same team which worked on the R400, might of course have more features than the original R400 design had, because, well, it'll only be launched in Q4 2004, best case scenario. The R420, which is based on the R3xx design with, of course, many tweaks, is to be launched in H1 2004, probably Q1 in fact. The estimated tape-out date and the transistor count are unknown.
Source : NFI