Well, I can only say, the only person I know who did handle a pre-production camera signed a contract which (in my understanding) prevents him from making any public statements comparing the camera to competitor products. And this person is an internationally acclaimed photojournalist whose name is probably familiar to many forum readers.
It's difficult for me to reconcile that this person can't make public comparisons, yet BOTH Nikon AND Canon for some oddball reason are in the habit of routinely giving ALL (!) their top-line pre-production cameras to some kids in Germany (with poor reputation for allegedly faking videos, no less) -- so they can post low-budget, highly-compressed, amateurish comparos to YouTube. Unbelievable.
And it further boggles my mind that many here want to make purchasing decisions based on said YouTube videos, and from other questionable sources.
Soon enough we'll see reputable, hands-on analyses from the likes of DxO, dpreview, Thom Hogan, Rob Galbraith and yes even our forum favorite, Ken Rockwell.
Personally, I think if you want a D800, go buy it. Same with the 5Dmk3. Their ISO vs. DR performance are going to be excellent, and more importantly, aren't going to affect your photographs one way or another.