Canon 5D MK III help required

[Squidy]

I'm no pro so they're likely pretty crap. I also learned that the 5D doesn't focus so well sometimes

[peety3]

I'm no pro so they're likely pretty crap. I also learned that the 5D doesn't focus so well sometimes

Your "old" 6D does have a surprising benefit: ability to focus in lower light than a 5D3/5Ds/1Dx (and probably the rest of the line...I don't know how the spec measures up across the line). However, in sufficient light for the system to operate, I wouldn't call it a speed demon, but it's a well-proven system and I suspect there's a combination of settings that conspired to make your life less focused.

[neuroanatomist]

Your "old" 6D does have a surprising benefit: ability to focus in lower light than a 5D3/5Ds/1Dx (and probably the rest of the line...I don't know how the spec measures up across the line)

The 6D spec is -3 EV, it's -2 EV for the 5DIII/1D X. One example of -2 vs. -3 EV is 1/15 s, f/2.8, ISO 51200 vs. ISO 102400. Personally, I don't think there's a meaningful benefit of that extra stop of sensitivity for typical shooting.