Nice shots, canon eos! I have to say that the clarity of your shots is tempting me big time to spring for the 400mm 5.6 prime.
The Canon 400L is a jewel of a lens. When I bought it about 18 months ago I didn't fully realize the position it has in the world of photography. I knew it was very good as far as quality and performance, as endless reviews and testimonies attribute that, but there is more to it.
It is quite*
inexpensive, for a lens in its class, at about $1300. Whether Nikon or Sony or Tamron or Sigma (and so on), none have a lens like this which (1) is tack-sharp used wide-open, is (2) reasonably light enough to hand-hold, and (3) is at the near-$1000 price range.
No, $1300 is not inexpensive. But try to get a comparable lens and, well, you get the picture!