There does in fact seem to be an issue with the D800 that we are just coming to understand. At ISO6400 and above, thermal noise will begin to predominate at higher shutter speeds (e.g., 1/80th). It manifests itself as a consistent blue-magenta cast over the entire frame, with some localized maxima. You can almost get away with ISO6400 out of camera if the subject is evenly lighted. In dark scenes though, you will just start to see a cast. Boost one stop to ISO12800 equiv, and it will be too much.
If you use live view, it will be quite a bit worse.
Interestingly enough, with a simple dark-frame subtraction, you can mitigate this noise to a negligible amount. In fact, this works so well, that it's hard to understand why Nikon didn't implement this option as an extension to "long exposure" noise reduction. Even a single library black frame, matched for shutter speed, gain, and WB, will do the trick very well. I guess "long exposure" is a relative term if the sensor is hot enough.
With the dark frame subtraction remedy, the camera is again amazing, and really does claim a place alongside the D4. I suspect we will learn some new ways to massage this data to make it look even better. Interesting camera.