Congrats! I am sure you will enjoy the new glass. Post some photos when you get a chance as I am sure the community would love to see you enjoying your new prize.

Just some food for thought...I have heard that you can focus with the 400mm with a Kenko or Tamron style 1.4xtc using anything but the middle focus point if you want to add some additional length to your lens. It would make it a f/8 lens, but sometimes you go that high anyway. Camera shake does become a concern at that point, but with a monopod I am sure you can compensate. I haven't read much on the subject here, but on Fred Miranda and POTN they talk about doing this.