Andrew over at EOS HD mentioned he'll be doing a shootout of the D800 soon so stay tuned for his comparison since he posts still images of frame grabs which is the proper way to compare video short of the original mov file.
Meanwhile I would refer anybody curious about the uncompressed HDMI out (which is far more interesting than the resolution) to this video (download the original and not the vimeo embedded video)
Man... Great demonstration of that extra tiny little bit of quality you can get when you're not relying on the internal codec. Canon definitely screwed up by not giving us clean HDMI out. I'm SO happy actually, that Nikon did in the D800, because just that could be the impetus for Canon to do the same via a firmware update.
Now I just wish Nikon had added zebra and focus peaking so Canon would also have to follow suit with those as well. heh
Canon has become such a sad follower, all they ever say is we see no need to do this or that until we see someone else bother. That is sort of attitude that sends companies on the long slide down. Instead of having the 5D3 hti up all the video sites by storm they leave out silly little costless things like focus peaking, zebra stripes, 1920x1080 1.6x cropped mode, etc. etc. and instead of getting amazing press and taking video world by storm again they get "meh" after "eh, ok". For what? To try to protect some $20,000 C-line??
It probably doesn't help how out of touch most Japanese electronics management has become, read some eye opening stuff about how insular they are and how they won't even employee student who decided to go to college outside of Japan, never mind if is Oxford or MIT, and if a younger employee knows that an older one is talking out of date rubbish, even if they try to bring it up in the most gentle terms, they get admonished and black listed as trouble makers.