All great points guys. As a former 5D Mk II owner and current 5D Mk III owner, they're great in low light. One other thing to add to the discussion is remember the lens matters too. Max ap lenses of f/4, f/2.8, f/1.2, etc. tend to focus faster, especially on the 1D Mk IV than narrower max ap lenses. Consider the 300mm f/4L lens on the 1DX vs. the 300mm f/2.8L on the same camera body. The latter will focus faster. Of course, stationary scenes who cares.
Had my 70-200 2.8II on the whole time. Great, fast combo.
5D III + 70-200 f2.8 IS II = a gift from heaven
I have to agree with you on that one. I shot a bunch on the weekend and was amazed how fast that combo was. I'm liking not having to use flash.
I tested the lens today in bright sunlight, with a B+W UV haze filter on 10 shots and without on 10 shots and noticed no difference at all in IQ. The only thing I noticed was in the extreme corners darkening with the UV filters on, but most of the image was not different at all. That lens is sharp! All tests done on a 5D Mk III.
Next really stupid question: Get ready. How do I post photos on here for destructive criticism?