related topic: "MORE AFFORDABLE AND REASONABLE FAST CANON RF TELE LENSES PLEASE..."
I used the EF 100-400 II already with a fringer adapter when I was still a Nikon Z user and I found it one of the finest tele zoom lenses I ever used.

and a 100% crop of the above:

Super sharp, very fast focusing, very close focusing, very well build and more, and taking TC's over the whole focal (*).
For the same reason(*), I keep my EF 70-200 F2.8 III rather than go for the RF version.
Since I had my R5, the 100-400 II really shined...


...but I found it too heavy for long hikes and sold it to go for the fantastic RF 100-400... A great lens in good light but F8 @ 400 mm and no pro-lens-AF speed...
After one year with the RF 100-400, and searching for something faster, I rented an RF 100-500 at Audiophil...
But after a couple of days with the RF 100-500 I found it not to be any sharper than my RF 100-400, I expected faster AF speed and it is F7.1 @ 500mm

A day's session with swallows in flight gave me too few keepers...


For what it is, I find the RF 100-500 very overpriced

Finally, I bought an EF 100-400 II again...
I'll keep the RF 100-400 for long, sunny hikes.
This is just my personal opinion and experience, no statement whatsoever...
Thanks for reading,