Did you use electronic or electronic first curtain?
Any distortion with BIF? Any slow down with mechanical shutter with the 600 + TC as that is not on the official list for 12fps.
There is no slow down but I do have the ver III so not sure if that matters with ver II. H+ is available in all combos I used so far. As far as distortion it did show up in some hummingbirds but with seagulls and terns today they had no distortion. Most things will be fine, depending on speed, wing placement etc. I took some dragonflies and they had a little but they looked really good.













