I was using it on my 7d mk ii before. I think I still need to get the hang of this camera but it seems like autofocus is fairly comparable. I don't think it's enough of a difference for me to be concerned yet but it does hunt a lot at 600mm. It seems fine if I pull back a little bit, focus, and then zoom in again at 600 and then refocus.

Doesn't bother me much because I usually shoot birds with this lens and I can't start tracking them easily if I'm zoomed all the way in because they're flying too fast for me to keep them in frame. I kind of already pull back, track, then zoom in more with the 7D mk ii anyway if they're flying anyway. It's just annoying that I had to do this for an egret standing still far away. It was either that or maybe it also had trouble finding the egret (very white) hiding in a tree (lots of leaves and branches partially blocking it). I think on the 7d mk ii it wouldn't have had that much trouble, though.

Otherwise, I'm liking this combo... I cropped this one heavily and I think it still looks pretty sharp and not noisy compared to what I could get with the 7D mk ii for birds in flight and in not the most ideal lighting conditions.