Just curious, if AF is 2nd most critical next to IQ, why do you think the EOS-M would be better than the T2i?
Actually, that is fulfilling a different need (a need for something compact, yet high quality). I think the EOS M uses the hybrid live-view focus mode so I'd expect it to be more accurate, if a bit slower. I don't imagine it would be any slower than my P&S, which can already take a couple seconds in dark settings...but the IQ upgrade (and the additional photographic controls) would be welcome by me.
As for the 5D3, went to play with one again at the store. Love it more and more. This time, actually got a decent lens (Sigma 50 1.4 I think) put on it. Ran some tests at high ISO and tested the AI Servo a bit. wow is all I can say. Up to 6400 perfectly usable. Even 12,800 is usable although quality degradation is visible. This alone would be a HUGE upgrade over the 60D which just squeaks by at 3200. Also, 5D photos appear much cleaner and more crisp when compared to my 60D (except for shots at ISO 12800 and 25600). 60D/APS-C has a more "digitized" look in comparison IMO. The Servo performance was just ok, perhaps even mildly disappointing- but I've seen how complicated the AF system is so perhaps have to spend time tuning it. The lens being 3rd-party might also have something to do with it. I bet/hope it would be better with Canon's L lenses. (As an aside, I ran into a really strange yellow banding issue I've never seen before, but apparently it was caused by the store's fluorescent lighting tubes)
Yeah, so if I can get a deal on the thing...might go for it. I've decided that EVENTUALLY it will get done (upgrade to FF)...but there are some lens changes that have to be made (give up 17-55 for 24-70, replace 35 with 50) and with the 5D3 price, can't afford to do it all at once. Looks like the 24-70 isn't even widely available yet anyway...store didn't have any, and haven't really found any on the net.