Does the following sound a good option
70-200 f2.8 L
EF400mm f5.6 L
and either a 1.4 or 2 teleconverter
As far as I know, both of these lenses are very good. I have the former lens in the IS version, and I'm very satisfied.
The 400mm f/5.6L is something I only know from reputation, which seems to be good overall. But keep this in mind:
It's not a fast lens, and with the TCs, it will definitely be slow. That may or may not be a problem for you, since it doesn't come with IS.
Unfortunately, your alternatives -- the f/4 DO IS and the f/2.8L IS -- are several times the price.
If you can live with the bellows of the 100-400mm, consider that one. Or consider the EF 300mm f/4L IS (the f/2.8L IS is optically superior, but also more than three times the price).
And, as others have suggested to other people looking to buy expensive lenses: try to rent each of your alternatives for a few days, check them out and figure out which ones float your boat. Only you'll know what you'll like.