(Another late to the game post for me) I don't do much in the way of events these days, but I believe in either backups or multiple lenses at the ready, so I'm always showing up with (at least) two cameras. After living a life of mixed crop factors (1.3x and 1.6x in the beginning, moving to 1.0x/1.3x/1.6x and 1.0x/1.3x), we're now (essentially) all-FF and I find that to be so essential to my sanity. Having mixed crop factors means lens changes take a lot of thinking, and sometimes become more complex than they should be.

These days we have two 1Dx, a 5DsR, 5D4, and a 5D3. The 5D3 spends most of its life at my parents house with our 100-400 in case there's some wildlife my dad wants to capture. For my studio work, it's the 5DsR first with the 5D4 as a decently-capable backup. In bad weather, it's the 1Dx bodies. Otherwise, the 1Dx bodies kinda collect dust unless I need the responsiveness (I'm not a high-frame-rate shooter but respect that these are so freaking responsive) or the spot metering with a non-center focus point; otherwise, it's the 5DsR and/or 5D4.