I don't think i've seen a sharp example from the 5D3 yet..
Just looked at Bert Stephani's shots straight out of the camera at full size and they look sharp to me, once you find where in each composition he focussed at f/2.8 that is, causing everything else to go OOF.
No doubt it would have been more valuable for analysis if he'd shot a couple of f stops more toward lens-optimal and used at least one of those many focus points on her eyes, rather than on the random elbow or dress or whatever, but the sharpness is there, nonetheless.