Absolutely backs up my assumptions and makes me glad I made the jump to Canon and bought a 5D MK3
These two points listed (and the diffraction issue) are why I gave up on Nikon.
It's not that I think the D800 is a bad camera, it's just not the great all-rounder I wanted but the 5D MK 3 apparently is.
I'll get mine tomorrow and find out first hand...
From the DPREVIEW article http://www.dpreview.com/articles/1690347434/first-impressions-using-the-nikon-d800/
I have two other issues with the D800, but it's hardly fair to call them criticisms, since both are a natural consequence of the massive pixel count. Firstly, on a 36.3MP sensor, accurate focus is essential, since there is less margin for error than you'd expect from a 12, 16 or even 24MP sensor. When viewed at 100%, even minor focussing errors are visible in files from the D800 where they might go unnoticed in cameras with a smaller pixel count, and although I've been impressed by AF accuracy on Nikon's prime and zoom lenses (so far) if you're shooting at wide apertures - especially on longer lenses - accurate focussing is a must.
Secondly, the D800's files are massive. It isn't unusual for high quality JPEGs to take up around 30MB on a memory card, and the .NEF files are bigger again. Not only will they rip through hard drive space like there's no tomorrow, but manipulating files this large on a computer can be pretty time-consuming. If you're planning on purchasing a D800, some extra RAM for your PC should probably also be on your shopping list...
Wow, you probably should have done your research. On the D800, each mode (FX/1.2/DX, etc) has a small/medium/large resolution setting. You could shoot in FX 25MP and be pretty close to the 5DMK3's file size and focus requirements.