While I have been taking a break from my work as a food photographer, so I have not done any studio shots on a tripod with Zeiss glass on the 5d3 yet... I can say definitely say that I am getting super sharp images from this camera handheld.
I shot almost exclusively prime lenses on the 5d2 until buying the 5d3 kit and I'm getting tack sharp photos with the 5d3 and 24-105 handheld. Whether or not this is just the improved AF system giving me more and better keepers remains to be seen, but I am extremely happy either way.
I'll be working on a food project in the next two months, so I'll see how it performs there, but I honestly can't imagine a noticeable difference, other than what I feel is much better color rendition in the 5d3, especially for vibrant colored food.
I also did a reshoot with the 5d3 of a scene for a feature film I shot on the 5d2. Video sharpness looks identical out of the camera to me as I was not shooting a scene that would have a lot of aliasing. Any perceived extra sharpness in the 5d2 was most likely aliasing on fine details like brick and grass. I am quite glad this is gone as the aliasing and moire can really kill the filmic look. With the ability to slightly sharpen in post, the 5d3 definitely edges out the 5d2 in sharpness (but not amazingly so). The high ISO video quality is absolutely astonishing though. Yes, the video can start to get waxy looking, but I can push the ISO so much higher now. I would have to use Neat Video on footage on the 5d2 above ISO 800 which would make the footage very waxy anyway and add a ridiculous amount of time to the render.
There are two tricks you can use to get rid of this waxy look of noise reduced high-ISO video... 1. Light your scene better and use a lower ISO! 2. Add film grain in post. My last stage of video processing is adding real 35mm film grain scans by Gorilla Grain over top of the video. While it may seem counterproductive to reintroduce noise, I think that ISO noise is ugly and film grain is not. Of course your taste may vary... but even at only 50% opacity, this film grain will "dither" your video and effectively cover over that waxy look.