I'm back. Had a good 10 minutes with 5D III. Q&A didn't go too well with two of the reps, kept on telling me the 5D had Firewire.
So, the sensor. They had memory cards in which was good. Set the camera to RAW, turned off all noise reduction. ISO 800 clean, ISO 1600 getting very noisy, ISO 3200 is very very noisy. No banding that I could see. No weird halos. Any better than the 5D II, not really. I have been trying to think of a camera to compare it with, thinking the 7D, or the 800D, but no. I have to compare the difference as the old 40D and 50D. Take the 40D being similar to the 5D II, and the 50D to 5D III. Technology wise, they are similar, edge to edge micro lenses etc were introduced int he 50D. The Canon 50D was advertised as being better at low light than the 40D, the 50D had a higher pixel count, and in real world shots the 50D was no better. I feel the same with the 5D III. Bad news, pixel peeping, the D800 was cleaner at ISO 1600 and faster. I wouldn't say it was no more than 1 stop better, half a stop at most, D800 1/3 a stop again.
Build quality, didn't feel as rugged as the D800. Would have had a better answer to this if I did a few drop tests, but I didn't do this.
Video out. Same as the 5D II. No RAW out via HDMI, mirrors what's on the rear screen. No crop mode, and no drop frame!
The AF and AE are not unified to work together like the 1Dx, or the D800 and D4. It cannot do some of the more advanced features. AF is good, tried a 85 f/1.2 and 50 f/1.2, it never missed even when choosing an out of centre focus point. At f8, told the AF does not work at all (reps seemed out of their depth to really answer), and certainly no tracking. AE was like the 7D, hit and miss.
In conclusion, the 5D III is a full framed 7D. There was no answer to the price, especially when compared to the D800. I think the reps knew this, but couldn't answer it publicly, I think the look in their eyes said enough. D800 has the edge in all areas, but IQ on the D800 may be just as good, if not slightly better. It is not a low light camera, the same is said for the D800. I was there with my photographer, met some other pros who shoot Canon. They felt bitter about the 1Dx and its price over the D4, and they won't be rushing out to replace their 1D III's.
I can't say much about the 1Dx as I have already had a day with it, not under an NDA but I have to play nice.