R5? R6? Anyone?

[Duppie]

Those are good questions .... wish I had precise answers

I will have to see if cropping a full frame image in post is equivalent to shooting in crop mode, I have not tried it yet.

I would say that the eye tracking is definitely better with a larger subject in the frame and absolutely the file size is smaller. The files are similar in size to a 17 mp camera. (ie the original 1Dx was 18 mp)

Composition is improved as the field of view is equivalent to a lens with 1.6 X the focal length of the lens you are using. Thus my 600mm lens will provide a field of view similar to a lens of 960mm.

I did some test with my R5 in my backyard on a sparrow. The bird was sitting about 30 ft. away. When having "Cropping/aspect ratio" set to "FULL", the camera could not detect the individual bird.
When I set it so "1.6" it was able to detect the eye of the sparrow, or head of the sparrow in case the sparrow looked away.

This may be a valuable option if you were planning to crop significantly after the fact. Downside of it would be that it is less forgiving in your composition, as there is less to crop.