First outing with the 100-500 this evening, so these are shot at higher ISO levels. These are all pretty decent crops using CRaw. One thing I notice is this lens AF faster than the adapted 100-400 lens and the 100-400 AF on the R5 is no slouch.
Did a casual handheld test on the R5 of the bare 100-500 @ 500 enlarged by 140% in Photoshop versus with the 1.4x TC at 700. Detail is almost identical, but noise is a little lower with the TC (no 3rd party NR applied to either).
I don't think I'l be using the TC on the 100-500 any longer unless I need the subject to be larger in the frame to aid the eye-AF in acquiring the subject (small birds, etc.).
Another thing I noticed was the IS/IBIS was less successful in stabilizing the shots with the TC attached. Comparing 140% enlarged 500mm shots versus 700mm with the TC, more of the TC shots showed unsuccessful attempts at stabilization.
On the R5s @ 90mp, I would imagine the results from cropping may surpass using the TC as far as detail is concerned.
In the comparison below, I had to zoom in to 500% in Photoshop to be able to illustrate where the TC shot looks a little better. At normal viewing sizes all the way to 200% magnification, I couldn't tell them apart.