Jeff USN Photog 72-76 wrote in post #19129658
I do find I can crop more on my 5D IV vs my 7DII, so "know" the R5 will have more ability to crop
What does that mean? Practical cropping needs a situational, focal-length-limited context. The real need is to get a quality image with whatever sensor area winds up getting used for the final displayed image. The two main sensor qualities in that regard are pixel density and noise per unit of sensor area. The 7D2 is only inferior to the 5D4 in one regard there; deep shadow noise at low ISOs, because the 5D4 has the on-sensor column ADCs, and the 7D2 does not, but has the old off-sensor ADC scheme. The high ISO noise per unit of sensor area is almost identical (actually superior in the 7D2 in incandescent white balance conditions), but the 7D2 has 1.7x the pixel density, or "pixels-on-subject".
It seems like you are talking about either using a percentage of the entire frame, or 100% pixel views, in which case the 5D4 will always give better-looking results if you ignore subject scale, but there is no practical reason to approach things that way, because "cropping" implies focal-length limitations, in which case starting with a larger sensor area is moot. If you can get closer with the 5D4, then yes, your crops will be better, if you keep the aperture wide open, with the same lens, but that is not a cropping context.
I think the main thing is will the Animal Eye AF on the R5 give me more hits against a cluttered crowded background of trees when the birds are 100-200 yards away
It should do a better job just telling what is standing out from the background, period, even with animal AF turned off. DSLRs have a lot of blind AF area in the frame, unless a high-res metering sensor is used for auxilliary AF, as is done with the 1Dx3. Even the 90D (which many consider a BIF dissapointment) starts hitting small things in the foreground consistently in Live View, where the sensor is used for AF.