Awesome, that's good information. Thanks.
I don't see myself needing to carry the 70-200 with the 7D mounted, in the bag. I should be able to get by with the camera mounted to a smaller lens, and having the 70-200 on it's own. Generally, if I have the 70-200 mounted, it's on a strap around my neck. My whole objective with the casual bag is to have something just big enough to serve my need, and no bigger. So I think the Retro 10 sounds about right. Thanks for the great assessment.
I have the Restrospective 20. While it can carry my gripped 5D with the 70-200, I find the other compartments to be too deep for my other things. I often find myself digging inside to find stuff. If it were possible, I would want to switch for the 10.