Help a Birder choose a Canon kit....

Hi all. I'm a longtime Nikon shooter, and although I don't plan to "make the switch" to Canon, I am thinking about replacing my current Nikon walkaround birding setup...a D7000 w/ 70-200mm f/2.8 plus TC-20III (for a 400mm f/5.6) with a Canon 7D w/ the 400mm f/5.6. I also may eventually move up to the 400mm f/4.

I am not new to the "exotic" super teles. I currently shoot a 400mm f/2.8 on a Gimbal head with my D800, but that is not nearly hand holdable. Unfortunately, Nikon does not make a 400 f/5.6 or f/4 prime prime. Although I'm getting there with the 70-200mm w/ 2x tele, the results are not even comparable to the 400mm f/2.8 (for obvious reasons).

Can anyone who uses either of these combos please comment on your experiences, or if you think there is another Canon body I should consider over the 7D as far as capturing birds in flight?

Thanks,