From these samples I would say that ISO 6400 on the 5DIII looks a lot like ISO 1600 on my 5DII, which makes me extremely satisfied. Looks like Canon actually delivered the promised two stop improvement. Based on those samples the highest I'd be comfortable using is 12800, but that's incredible. Another thing I noticed is the apparent absence of pattern noise even when I push up the exposure, which should help improve the usable DR as well. Maybe this is because they were shot as JPGs and not RAW, but I'm optimistic.

Couple the improved ISO performance with vastly improved AF and 7D-like body and the 5DIII is everything I ever wanted in a 5DII upgrade. All the other features are just gravy. Really looking forward to this camera.