Picture below was shot at f11 with 250W studio light, not the best but it does show how sharp the 5D III can produce.
At iso 100 like your shot you hardly need a 5d3 to produce a good result (actually the 5d2 is said to be a bit sharper at low iso due to the weaker aa filter). Esp. for studio shots putting money into a sharp lens might be smarter than the newest camera body...
The jpeg iso samples of dpreview are to compare noise, in the way that you can see what's left of the details after nr
. I guess dpreview is a reliable site and they had the same setup, and imho the 6d is indeed visibly better in these shots (detail left and noise in background) - I just loaded all into lightroom and compared them side by side.
So either Canon at last really did something about their sonsors (rejoice!) or the 5d3 shots were done with an older firmware version that had a worse in-camera jpeg converter - we have to wait for a 6d software raw converter and raw shots to be sure.