I know we aren't supposed to compare images taken on different bodies, but, doing so anyway, it looks like the Nikon is better at shorter focal lengths, but the Canon is killing the new Nikon at 400 mm. At least to my eye, they are pretty even between 200 mm and 300 mm, with maybe a slight edge to the Nikon

While I see the new Nikon as much better from 80-135 mm and roughly even 200-300 mm, greater than 95+% percent of my shots are at 400 mm, so I'd still pick the Canon. Granted, I really hope that Canon updates the 100-400L.