I currently have a 70-200 f4 (non-IS). It's a great lens and very sharp. I also have a Canon 1.4xii that pairs well with it.
I enjoy shooting architectural details, landscapes and BIF. I used to have a 400mm 5.6 for BIF but sold it because it was an expensive lens to have sitting around for the odd time I could get out and shoot birds. I also didn't like that it was a prime lens so missed being able to zoom out a bit when in the field and would see nice landscapes.
I've been toying with the idea of selling my 70-200 and putting the money towards a 100-400ii. From what I've heard it would be good for both landscapes and BIF. The main drawback as far as I can see is that it's quite a bit bigger and heavier than my 70-200.
Has anyone else made a similar switch? Maybe I'd just be better off keeping my 70-200 and throwing the 1.4xii on when I need a little more reach? Realizing of course that 280mm is quite limiting for BIF but can get some decent perched shots.

