I TRIED to get the XT-2 to fail here: lens a shade under wide open, westering light, shooting a RAW at ISO 100.

You notice I include the 100% crop of the duck: not a good composition, nor supposed to be:

I was wanting to see again if I could "grab, press back-button, lock and shoot" even as I was aware this duck was half-airborne in mid-squawk ...so locked onto its head with the tiniest AF point from 35 feet away, camera still panning as I pressed.

Well: it's at f1.6, at the slowest and nominally contrasty ISO 100: I think this would have been beyond the Canon 1DsMk2's ability, and I have to say the XT-1 would have been by prayer only.