10 minutes isn't enough time, and the reps were not very helpful. I'm sorry about that!
If it was a trade show or private viewing my answers would have been better. I've worked at plenty of public exhibitions and an exhibitor for Arcam, Fujitsu Plasmavision, Monitor Audio and Birmingham City University. Worst three days you'll ever do in your life!
Noise, acceptable for what, it depends on the output, that is the answer. ISO 1600, or even 3200 is fine for most things. 800 was silky smooth and wouldn't require any post noise reduction, 1600 there was some luminance noise, 3200 luminance and chroma noise so I would add noise reduction if I was to make a large print. 3200 or even 6400 would be fine for editorial work for news print. It's not a low light monster like the D3/D4 or 1Dx.
There is not much I could have done when indoors. I pointed it at the skylights and checked shadows in the roof space, looked at areas under tables etc. I couldn't do anything like push shadows in post to check noise for banding etc.
Answer your question to what am I used to. My only dSLR is a 50D. I do not like to use it above 400 ISO, and pushing shadows even at ISO 100 introduces banding and cross hatches. That is my acceptable level. I still shoot 135 with my Contax too. My main job is a boom op, and when its down time I work as a photographic assistant in ad and corporate work. Sometimes the 5D II appears, if not I'm used to 900R, D21, Red One or F35. When I'm working in stills the cameras and backs I'm used to working with are D3, D3x, 1D IV, and mix of 645's with Phase One or Leaf backs. Photogs I work with have the DSLRs for low light or low res, and the medium formats for studio or when larger res is required. 5D is a middle road, and so is the D800, so is an odd camera for them to justify. I have shot several times with the 5D II, I do get them hired, and it has the same AF as my 50D. Any new AF system to the 5D is a godsend. Shooting with a 85mm f1.2 and using a out of centre focus point most the time it is out of focus even in good light, and sometimes carries on searching. In low light I wouldn't rely on the 5D II at all. Is the III AF faster, you bet-ya! The 5D is Canon's only answer to a studio camera now that they removed the 1Ds, poor AF was the only thing stopping the 5D from being used by many. I'd hate working as a DIT with a 5D II, checking each photo as they came through and noticing the are all looking soft, you wont get that with the III as it will get focus most, if not all of the time.