I can't imagine any D700 shooter being displeased with the D800.
4fps is still very fast and would not often make the difference between success and failure in most cases. Not a whole lot happens between one quarter second and the next. I get that may be the difference between a baseball approaching the bat and the ball hitting the bat.
It would be interesting to see a 2 second burst at 4fps and a 2 second burst at 10 fps. Shooting something like a baseball hit or a run up to a basketball net. Just to see how much difference there is in the shots.
I just hope my D800 arrives before March 16. I know the release said late march but the local camera shop says Nikon says late feb in the stores information.