For ISO 10,000 and above, I think I'm doing ok for a beginner and the K-5 seems to be a bit better than "marginal", in my opinion. I try not to push it, but I'm doing ok in that region, but would like to bring it back down. The main issue I have wtih ISO levels that his is when the performers use heavy smoke and NOTHING will work. Not even the pros I'm friendly with and shoot with in the pits, on their D3's and 5DII/IIIs are able to get past that. It makes the noise look worse.
I could shoot with a faster lens, sure, but then I'm dealing with DOF issues.
I didn't know the IIs was reported to have a 1 stop low light advantage. I thought it was purely sharpness and AF performance. This is the first I'm hearing of better low light performance.
THe FA35 I use with AF. I have considered the FA77, especially since I like very sharp renditions, but I have to justify the usage. It might work, since I find the M85 too long (as mentioned, I have stage, pit, and backstage access), so I have to continue learning and moving forward and seeing where my needs lie. I might end up sacrificing speed to just get a Tamron 70-200.
Both at ISO 10,000: