Unless "R600" represents a weird shifting of project names, or is a project running concurrently for rather than--as we expect--after R500, I don't see how Xbox2's chip would wear that moniker best. Is X2 indeed slipping well into 2006? Is R600 perhaps a project attempting to see how an eDRAM-laden card would do in the PC marketplace or in other sectors, and that's a more-determining factor? Or an alternative-designed product that's not really "the generation ahead?"
Considering that it seems like R500 will be released around the same time as the Xbox2 (at least by many assumptions right now), and quite possibly a lot after, considering X2's GPU would have to be solidified and produced in might higher volumes to assure a good console launch. But that chip will be the next designation up?
It seems much like "R600" is meaningless at the moment, as everyone expects what it would/should be representing is "the next-generation higher architecture to R500" aimed at the PC. (Which can, of course, have variations elsewhere.) If it's NOT... well, then we need to know what it is first.
Hopefully May 5th will indeed bring some clarity, because at the moment there's not much of it as far as this is concerned.