Great shots Steve, and nice to see some examples og the 100-400mm.
I found it an invaluable ally on Safari in Kenya, both at 400mm for distant animals, but also at 100mm for closer or bigger subjects. That said, all of the following were taken at 400mm, using a Canon EOS 350D. So effectively operating at 640mm. All images below are uncropped and unretouched JPEGs from the camera.
Above: Canon EOS 350D / XT with EF 100-400mm L at 400mm (640mm effective), 1/160, f5.6, 200 ISO
Above: Canon EOS 350D / XT with EF 100-400mm L at 400mm (640mm effective), 1/1000, f5.6, 400 ISO
Above: Canon EOS 350D / XT with EF 100-400mm L at 400mm (640mm effective), 1/40, f5.6, 800 ISO
I was impressed by the IS on this lens - remember traditional photographic advice would say for an effective focal length of 640mm, you'd need a shutter of 1/640, but there I was shooting as slow as 1/40 out the top of a jeep for that monkey in the tree (who thankfully sat still). That corresponds to 4 stops of compensation...
I still didn't get on with the push pull design though...
Gordon