Here we have two creatures that can see in the dark. Demetrius the cat, and the D800. Dark is an understatement. We're talking f/1.4, 85mm @ 1/30th sec, and ISO 25,600. What's more impressive than the low-light handling is the fact the AF locked on with absolutely no problems.
Versus the D700, when downsampled to match, I'd say the D800 is around 1-1/2 stops better. If I nail the exposure, I would definitely feel comfortable with a 25,600 image at 5x7... *maybe* 8x10 if the stars were aligned. I'd say I felt this way about the D700 at ~ISO 8000.
But, that's relative. I say that about the D700, but in practice I would *never* go above 6400 because of the loss of detail. Noise I can deal with, but the problem is that images start to look soft on the D700 when that high. I mean, check out the whiskers in this shot! I'd say it's easily TWO full stops more usable... if not 2-1/3rd.
SEE IT HUGE: http://www.flickr.com/photos/seanmolin/7028040701/sizes/o/in/photostream/
This sample has been downsampled to match the D4's 16.4MP. Be patient as it is 14MB.