All these 35mm DSLR's have pretty similar IQ at reasonable ISO's.
Nikon D800 | ISO 100 | 1/100s @f/11:
Canon 5D Mk III | ISO 100 | 1/100s @f/11:
... and that's at 800px web size
Inevitably, someone's going to wonder why I severely underexposed the photo & then lifted the exposure; rather than getting into the logic of why I did that, I'll just post the following comparison, where each camera was exposed so as to not clip the red channel in the sky near the sun. Shadows were then lifted to reasonable levels for viewing:
First, the full-frame images:
Canon 5D Mark III:
Now, let's view them side-by-side at 100%, w/ the D800 downsized to 5DIII size for easy/fair comparison:
Please view it at 100% here; else you won't fully appreciate the difference: http://cl.ly/JipE/NikonD800_vs_Canon5DIII-SunsetDR.jpg
For certain types of photography, this matters. For others, it doesn't. Beautiful photographs from the previous posters, btw. Despite the results of these comparisons I've done above, I stuck with the 5DIII
for various reasons since I find it suits my people photography better right now (AF accuracy/precision, wireless RF flash, love the joystick for AF point selection, cross-type AF points, higher FPS, etc.). But I wish it had a D800 sensor for when I shoot landscapes (using over $1k worth of Singh-Ray filters for now) or for those moments when my flash mis-fired or the meter completely underexposed an image b/c of a strong backlight, or what have you, & by the time I re-adjusted I'd missed the moment (and I can't salvage the underexposed photo because of noise).
In the end, we choose which limitations of a system to accept & work around, & which ones are unacceptable. I was still able to work around the limited DR of Canon & get these, for example:
But back to the topic at hand: it's great to know about advances in technology, & how they may help us achieve our vision. DXO's quantitation, to an extent, helps some of us do that.