My eagle shots once again necessitated 100% crops. That was with a 1.4x TC on the 400mm f5.6. The 6D autofocused at F8 to yield a less than 30% keeper rate. Next time I go eagle shooting, I think I bring along the 5D MkIII from school, just to see how much better the AF is. But what I was really wanting was a 1Dx/500mm f4 IS/2x TC III setup. Alas, my lottery winnings have yet to materialize.