To add to the IS/no-IS discussion. This was shot at f5.6, with a 1DX and 200-400 f4L IS 1.4x @560m. Shutter speed is 1/100s.
I do believe the majority of us would have had issues getting that sharp, without IS. This is shot with my flag bandoleer cradle, where I use a monopod as the flagpole, with a RRS tilt head on top. A setup I highly recommend.
Eldar, that's another great shot from the Ark - well done! I'll add to demonstration - here's a re-post of my barred owl photo - shot at 600mm (300 f/2.8 IS II + 2x III) at 1/30s, handheld with no support pointing up at the bird at a 60-75 degree angle. I think this shot would be almost impossible without IS as it's using all 4 stops and a bit more of it. Also, by the time I had set up a tripod, with or without gimbal, it would have been gone: