I covered a 5 day event with a 70-200 mkII hung from a Black Rapid Sport strap and it was great. I had my Retrospective 10 on my other shoulder with my 'other stuff' that wasn't as great. Awesome bag, don't get me wrong, but was uncomfortable for consecutive long days, on my feet and moving around in crowds. So, a few days after I got home, I ordered a thinktank belt and a few pouches and this is my new set up. I keep my 70-200 hung from the strap and extra lenses and/or a flash on my belt. Weight is taken off of my shoulders and I feel a lot more mobile. Depends on what you're doing or how much you need to bring with me. I had never considered a belt system before, but definitely found the convenience in it!