The D800 has some interesting features that i'd like to have, but the poor high ISO performance is not one of them. If it were 22 mp and had two stops better, It would be a tougher decision.
Why would it be a harder decision? In that case, if you liked USB 3, XQD, and the Nikon ergonomics *that much,* then maybe.
The Nikon D800 (and D800E) would be more compelling if it was able to offer a higher shot rate or higher ISO while maintaining the same large file size. If you don't need 36MP, you can always crop, after all.
Personally, can't wait until 36MP cameras are more common from Canon - especially when data rates are there to support it.