mwsilver wrote in post #16651915
On my 60D an ISO of 6400 is way too noisy in most situations. ISO 3200 is still pretty noisy, but much less so and can be fairly effectively cleaned up in post. As a general rule I try not to exceed 1600, and prefer staying under 1000 if I can. Based on my experiences with my friend's 70D, I could safely double all the ISO speeds I mentioned above. The 70D's ISO is between one and two stops better than the 60D. In fact, an ISO of 6400 on the 70D gives results that look almost as good as 1600 on the 60D. Actually quite amazing! The 70D's ISO at 12800 was noisy, but much less so than the 60D's 6400. A lens at f/1.4 with an ISO of 6400 or 12800 would allow you to capture images in extremely low light.
You are effectively claiming that the 70D is better at high-ISO work than the 5D2. I don't buy it. Not that I shoot either, but I can compare my 60D, former 5D and now 6D. I get two solid stops between the 60D and 6D, IF I DO EVERYTHING RIGHT. No way you're getting that kind of difference between the 60D and 70D. Head-to-head with the same settings, lighting and framing, I doubt anyone could see any difference at any setting the bodies share.
Personal tastes and tolerances certainly enter the 'max ISO' equation. I get quite good results out of my 60D a 6400. Printed 8x10 they look very nice. Admittedly, 12,800 is harder to work with, but done properly, very nice 5x7 prints are possible. I haven't printed anything from my 6D, yet. I don't expect to need 25,600, but my 6400 and 12,800 stuff should be easier to work with and yield better results than I get with the 60D.
Bodies: 60D, 6D.
EFs: 15-85, 10-22
EF: 28-75, 35 f/2 IS, Σ70-200 OS, 100-400L
Flash: 580EX II, 430 EX II