ISO 6400 looks great, granted these shots are not taken in ISO 6400 lighting so kind of hard to compare to the D700/D3 family. If the quality carries over it would be as good or nearly as good imo. Certainly very impressive and makes me hopeful that my wish to have the current FF high ISO performance (or close there to) in DX format to at least ISO 6400 will be a reality. Only another month or so until delivery!!
The 25,600 samples all look terrible as I expected, it is the 'a bad photograph is better than no photograph" setting. Even with some cleaning up they are usable as web sized photos only...or for taking evidence shots of 'big foot'.