I just took my standard test shots (sheet music) from across the room and compared to the 200-600, I am pleased with the sharpness and contrast.
I am a nerd and appreciate the time people take to do all of the scientific measurements, but good enough is good enough for me. This lens was an interesting mix of compromises and the kicker was that it is way less than what I was mentally prepared for, for an f4 lens, so I just bought it. Looking forward to my first soccer match with the new lens (unfortunately not until August).
Anyone interested in ultimate photo quality is carrying 2 bodies with a 400 2.8 or switching systems, no? I always find it weird that people are so demanding of a lens that no one is forcing anyone to buy.