Canon 100-400 vs 400 f/5.6L?

I'm thinking of the best long focus option in the range of 400mm. Can someone comment on 100-400 f/3.5-5.6L vs 400 f/5.6L?

It looks as 400 f/5.6 has a much better IQ comparing to its zoom peer:

http://www.luminous-landscape.com/reviews/lenses/forgotten-400.shtml

Is it so, or they might have tested a soft 100-400 copy?

I'm considering a few options:

1) 400 f/5.6 (#1 candidate at the moment)
2) 100-400 f/3.5-5.6L (too soft at 400mm, dust collector?)
3) 70-200 f/4 with x2 (IQ at 400mm looks worse then 400 f/5.6)

4) 300 f/4L IS with x1.4 (IS is nice thing to have, but again IQ is not as good as 400 f/5.6)

5) 70-200 f/2.8 Mark II with x2 (again it is not as good at 400mm, which would be the max limit unless combining a few extenders)

Basically, I am between (1) and (2). I'm planning to use it for outside sport and bird photography; IS would be nice, but I could probably live without it at ss over 1/600 anyway.

I would appreciate any comments.

Thanks!

Andy