Don,
What an outstanding 2021 achievement wildlife photography!
Imagine the weight of a 7D Mark II and 500 mm lens with a X 1.4 extender at 700mm or a 400mm with a 2x extender on that! Any combination would be 2.5 Lb heavier!
Also you likely have far more stops of IS, if you do BIF!
I would have loved to see this with the 2 X extender as you would LUT more pixels on the bird!
Any other gleanings from that shoot to share?
Asher