Calling a 512sp Fermi a GTX 580 would be in line with the AMD renaming.

Seriously, this rumor has been thrown around since the release of GTX 480. I still don't see anything concrete though, just guesswork. I suppose they will do a kicker at some point, but I doubt it's just going to be a 512sp fermi gf100b. That should have come out a long time ago, and in any case it would only be like 5% faster.