Not exactly a pro, but experienced. I still have my 1d MkIIn (same focusing) and 400mm f5.6 lens, although I haven't used the Mk IIn since getting my Mk III, the settings I used depended on conditions, how close and bird size for BIF.
A clear, uncluttered background and a small bird in the viewfinder and I would probably use all the focus points or the 11 especially for an erratic flying bird and to my knowledge, the focus doesn't exactly slow down, but technically a slightly, slower method as the focus point could keep changing as it tracks the bird. Bare in mind, using more than one focus point and the focus could be on the tail or wing for example where, ideally you want it on the eyes, particularly if photographing a large bird.
A more 'busy' background the center focus point has a better chance of locking on and, since the one focus point is always (hopefully) on the target, it's faster although you could keep loosing the focus unless you are very good at keeping the bird center frame.
I found the best thing to do is just practice at all the various settings to find what works best for you under what conditions, since so many things can effect the result.