The 5DIII looks over-sharpened, rendering the quality of the sharpness cheap-looking (Powershot-like).
The D800 looks more real, with plenty of room for careful pp-sharpening (see the photo of the 3 women in the middle of the test shot).
What is interesting is that the 5DIII has better contrast, while keeping good colour...while the D800 has a really off white-balance yet also appears to keep the colour (again, the 3 women picture being the 'real-world' colour reference).
This might suggest the D800 has issues maintaining accurate white-balance with natural colour-balancing.
Interesting...but I still much prefer DPR's studio-comparison tool, and hope they use only production models when the comparison is ready.