Nikon rates the "basic" ISO (before going into the HI category) for the D800 at 6400. Is there any reason to think that Nikon does not know the camera's capabilities? I assume that one may rely on the Nikon ISO ratings to compare the Nikon camera's low light capabilities. The "basic" rating for the D4 is 12800, 1 stop better than the D800 rating.
So far I have not encountered a landscape that was moving so fast that I could not capture it at 4 FPS. Obviously the D800 is not a camera for the sports photographers and photojournalists.
I see much to like in the D800 at a price that, in my case, will allow to avoid paying a lot of money for features that I don't want, e.g. the D4, and at the same time obtain more of what I do want, i.e. superb quality and detail. Of course I will be anxious to see the reviews after field testing. However, I am not aware of any Nikon camera that did not test out well in the field, i.e. verify the specs claimed by Nikon. Nonetheless I am eager to see the reviews.