Have a look here: https://www.flickr.com/groups/97933621@N00/pool/
Lance: perhaps you can chime in. I've never used a 400/2.8 but from my understanding, at this sort of FL you're always battling adequate shutter speeds and so the faster the better generally speaking but DOF is a lesser issue since if you can get close enough such that DOF becomes a big issue, then a shorter lens might suffice??