Interesting points from all of you. I do need to try Topaz...however mine is currently an older XXD body, not a 5D2.
Mikael, that's a good illustration of your point. However, in that situation, multi-shot HDR is really more called for, in my opinion. My body has a bit worse noise than the 5D2...hahaha. How would the D3s compare using similar under-exposed technique at low ISO, to the D800 (accounting for image dimensions, however you might want to do that)?
My cousin has the 5D3, and he mostly uses Lightroom 4 (although he has CS6). I tried to reduce some of the "grain" noise on a couple of his RAW shots done at around ISO 4000...on his computer using LR4. I must say, LR4 is far less effective at reducing that, than CS5 ACR is, on similar grain noise on my own files, done with my older body. Of course, those have similar amounts of noise way down at ISO 1250...haha. His files were exposed normally, not under-exposed. This grain noise seems to have a hard texture...sort of like you're trying to sand it smooth with sandpaper that is too fine. You can argue over which type of noise it is, I'll read it.
I can see why the D800 gets such high marks from DXO, but still, I don't think it tells the whole story. And ergonomically, the D800 is unusable for me. Also, I don't care for Nikon's lens lineup...especially their 135 f/2 lens. That alone would make me not ever switch to Nikon. Talk about a lens for old farts, looks like it was designed in the 1950's. There are plenty of other reasons too, of course.