Thanks Funkboy and Dustin. I am getting more familiar and trying different settings. The last couple days was fixed ISO (a realistic value), TV and appearature automatically chosen. This morning I tried Av with my choice of ISO and shutter speed getting automatically chosen. Shooting over water, then into the air or trees requires serious exposure changes and I have my Q button for compensation, etc, etc. I'd like to hear more suggestions relating to the highest likelihood of being prepared for anything, from anyone.
Today was 300 X1.4 (both are mark III) and I managed to get a similar teal framed to a similar size although all the various parameters are not identical and here's the result. I don't think the 600 shot is one of the best I've gotten, but it's representative. Today (teal2) it was overcast.
Teal_600 6D 300 F2.8 II 2X III 1000th F8 ISO 8000
Teal2_420 6D 300 F2.8 II 1.4X III 800th F6.3 ISO 3200 (coming next reply)
Clearly the edge is to the 1.4X although the ISO setting I guess favors it.