How is it for BIF? How many shots in those 6 hours? The 90D takes a while also to write a burst to a card. I am waiting for a UHS-II to be delivered but according to Grant in another thread that won’t cure the problem. Have you used the pre-burst mode?
Not many birds around here these days and no good weather, too.
Tried M6II + 100-400 II (hand held) for half a day.
Keeper rate was not good because of hand holding the combo and perhaps setup. Need to do more test with moving objects.
Some personal observation (qualitative assessment):
1. Battery life was acceptable somehow (one battery, half a day, about 500 shots).
2. Noise level worse than R. ISO 3200 would be the ceiling.
3. Obviously, reach for farther objects was much better, but because of shallow DOF keeping everything in focus was harder.
4. Focus acquisition much better than R with old 1.3 firmware.
5. Setting the AF start point and waiting for objects to enter it and then start tracking lead to more keepers.
6. Not all shots in a burst with tracking were in focus, about 2 of 10 rate. I did not try the pre-burst mode.
7. Writing bursts to UHSII card (rather old Lexar 1000x) was not that fast. Will tray faster Delkin V60 card later.
8. Camera was more responsive for opportunistic shots compared to R.
9. Viewfinder was a must but it looked flimsy, not as secure as built-in one and ready to be broken.
Below is a typical shot. Canon EOS M6 Mark II , EF100-400mm f/4.5-5.6L IS II USM
