Thanks neuro.

I was under the impression the EFCS reduced, but didn't eliminate, the jello effect. Still, if the readout speed is just 4x the time it take for the shutters to cross the frame, it's likely fine.

I'm aware of the lowered reach I'd get going full frame. I'm often already annoyed at the 70-300L's reach. But the image quality I used to see from the 1Ds2 was just so much nicer than anything the 7D2 spits out. The improved per-pixel quality will mean more crop ability to get some of that reach back. A 100-500 would more than get it back, and the ability to use an extender would pretty much cancel out the lack of crop too... so I'd have options and combinations... and I'd still have the 7D2 + 70-300L if I felt the need.

A forgotten concern when making my list was the lack of / reduced weather sealing on the R8. I'd prefer not to have to get paranoid about rain.

I doubt you have any EF-S lenses kicking around to judge the quality on the 9.4MP crop mode images, which really would only affect the 10-18mm. On the 7D2, I like to keep a fair number of pixels just because the individual pixels aren't the highest quality, and downsampling makes up for it. If the R8 gives 9.4MP of high quality pixels, then the lost pixels in the rare ultra-wide shot might not matter... Even if I decide the 10-18 isn't fit for use on the R8, the 24-70 will have become wider. Not as wide, granted, but probably a more useful range in most cases. We'll see if I feel a need to get a replacement ultra wide.

Typically I use the 7D2 w/ centre point AF, M mode w/ auto-ISO. The two wheels are shutter and aperture, and the thumb lever that normally defaults to AF mode selection I have configured for exposure compensation, for quick use when auto ISO goes dumb. If I have to use the M-Fn to switch the wheel between shutter and aperture, it's not the end of the world. The shutter and EC are the two I likely change the most often. I could likely live with one dial and the M-Fn to choose what I'm setting... or get the adapter with the control ring.

I'll have to search for some sample EF-S images, and see what the new Fv mode is. But you're making the R8 seem like a reasonable option (that gets me 1/3 of the way to 100-500mm in savings already!)