I'm another one that would happily shoots my 100-400, wide open, constantly and it gives perfectly sharp images. Given the varying temperments of the birds, and other critters, I wouldn't give up the versatility of the zoom for anything...except maybe a "Mk II" version, and eventually the 200-400 f/4 + TC.
Skagit Eagle-1104
Regardless of which one of those two you pick, though, you'll wind up with a monster system for capturing birds.


