A few comparison shots. I haven't really taken the time to AFMA the 150-600S yet, but it seems to be doing ok.
~100% crops (@400mm) of my neighbor's mailbox about 40-50 yds away.
Canon 5DIII
150-600S @ 600 mm, 1/640, f/6.3, ISO 640
150-600S @ 401 mm 1/640, f/6.3, ISO 800
Canon 100-400L Mk I. @400mm, 1/640, f/6.3, ISO 640...this was taken ~20 min after the others. The first set were so bad, I wanted to retest.