Hey David - welcome back! I think Brant and Joel nailed it with their replies. I moved from the 5D4 to the R5 over a year ago, and I have the RF 100-500 as well. The eye-detect AF is really fabulous for sure, especially with birds and people. It's not so great with other wildlife, but I'm sure it will keep getting better. I shoot in CRAW (compressed raw) all the time. It improves the buffer and reduces storage size without compromising quality. The R5 isn't perfectly weather sealed --- the viewfinder fogs up in wet weather, even when I use a rain cover. But it still works fine. I also own a 1DX III and I don't think I'll ever get rid of it, because I still love the OVF over the EVF. But there are so many advantages to the mirrorless system.