Rather than dragging up the old thread (which has stagnated) I thought I'd start a new one, outlining my initial impressions of the EOS R system. Hopefully it will help others who are tempted to make the jump to mirrorless.
Firstly, the size — It's tiny... and I mean tiny! This is good in many ways (my hands aren't the biggest and so it's a good fit) but it's a bit fiddly getting lenses on and off (both EF and the heavy/bulky RF 24-105). Initial impressions were that it wasn't particularly well built but in use it feels solid enough, though not as solid as my DSLRs.
I tested it with the EF 70-200 f/4 L IS II first and I must say I was very impressed — essentially native performance with the adapter means snappy AF (although no faster than my DSLRs) and excellent accuracy (better than my DSLRs), with focus remaining consistently locked and no hunting whatsoever. Even in one-shot AF the camera appears to constantly refocus on a subject so I'm not really sure what difference servo AF would make? One thing that did bug me was that the camera/lens continues to focus when the camera's idle, and I either had to turn it off completely or set it to a 15 second auto-off. Is there any way to stop this?
Next up, the RF 24-105. Lovely build and solid/heavy. I couldn't fully test it due to the limited range on a FF body but the images I did get were very sharp, at all focal lengths (even 105mm, a typically weak spot for such a lens). Focus speed was very good, although not noticeably better than the EF lens.
In summary, the AF is certainly more consistent than a DSLR once a subject is identified, and the camera did not once struggle in this area. Focus accuracy remains similar to that of a DSLR, which of course isn't a bad thing. Overall I was more confident in the RP than I am with my DSLRs, which is a great result given the very short time I spent shooting the RP. The speed of the camera in general is also better (compared to the 6D), with it feeling much faster than it actually is (only two frames faster in one-shot burst mode — not tried it in servo yet). I had no problems keeping a subject tracked and in focus in one-shot, which is typically weaker for moving subjects than servo.
Onto the EVF, which I thought would be my biggest issue. Not so, however. To be honest I didn't notice any real difference between using the EVF and the OVFs of my DSLRs — refresh speed seems good and there isn't any lag. I did have to turn the EVF brightness right up, though, and even then, in the sunshine, it was more difficult to see than an OVF. Luckily the EVF and rear screen are adjusted independently, so you don't get caught out as easily by incorrect exposures.
My biggest criticism is how the EVF freezes momentarily while the shutter opens; it's not too much of an issue when you're not holding your finger on the trigger but it makes the 'spray and pray' approach for fast subjects more difficult. I know some mirrorless cameras (Sony) don't suffer from this but presumably it's unavoidable in the RP? It's not a deal breaker and I did begin to quickly learn how to adapt to it but it is one of the few areas in which DSLRs emerge victorious.
Hope someone finds this helpful, and if anyone knows any ways to address the issues I've addressed please holler at me...