So I just had my first real play with the R5 down on the beach, doggie pics and some gulls in flight.
I am completely impressed with tracking of birds in flight and keeping up with automated tracking, eye focus etc. Amazing. I feel like decades of honing my skills to capture BIF shots with lesser AF systems is now moot.
Jury's still out, but I am pretty sure the 1DXIII is now irrelevant.
I was shooting 100-400mm II with 1.4x t-con. that alone is amazing and for decades I've kept zooms and t-cons separate. This combo just works perfectly. Now that I am so confident in this bodies ability to work with the 1.4x seamlessly, I also am no longer jonesing for the RF 100-500mm. I feel like I already have it plus 60mm 
I had some questions; 
- How do you program the button push on the multicontroller?
Am I missing something? I cant seem to find where I would program the "button push" function of the multicontroller. I did find how to set it to allow AF point selection. But I'd like the "press" button to switch it back to Center AF. Now I need to move my thumb down to the "SET" button to get the AF point centered again.
- Is there a way to set frame rate below max/20fps when in electronic shutter mode?
Part B, is there a setting to let you know when/how many image are being taken? lol. I may have shot 916 images 45 minutes when I really meant to take about 60...
- Is there a way to set the RF dial on my EF-RF adapter to adjust ISO AND initiate AUTO-ISO?
Let me clarify. On my EOS-R I have it set so that turning the dial increases or decreases ISO. When I turn the dial all the way down, it goes down to ISO 100, then to AUTO -ISO. with the RF dial set to adjust ISO on the R5, this is not happening. I can adjust ISO of course, but when it gets to ISO 100 and stops there. Is this not possible to set up that way on the R5, or have I just forgotten how I did it on the EOS-R? (likely)