A great friend allowed me to test his 200-400 today and I compared it to my 400 F5.6. On the camera, I was not sure that I had perfect sharpness, but in the computer, there was no question! Here are a couple of examples from our shoot this morning.
Nice photographs Kelly! We're you able to hand-hold this lens or did you use a Mono-pod? I've not rented this one to test yet. Do you like it well enough to sell your 400mm for it?