I would use two bodies (with a 15-85 and 100-400 presumably) before I would decide to carry a single bazooka lens (and a lens that does 560mm at the long end cannot be anything else, especially at f/5.6 aperture). YMMV. 
Actually I've done dual wield with a 16-35 and 70-200 and it's a great thing to do, very comfortable and adds a degree of failsafe.
(I've noticed that you're at exactly 1300 posts and I'm exactly at 900 now. LOL)
![[Image: RguqJtSH8r8.jpg]](http://cs619726.vk.me/v619726358/9c89/RguqJtSH8r8.jpg)
Actually I've done dual wield with a 16-35 and 70-200 and it's a great thing to do, very comfortable and adds a degree of failsafe.(I've noticed that you're at exactly 1300 posts and I'm exactly at 900 now. LOL)