I own the biggest LowePro. It certainly does the job, but when it's carrying 45 pounds of gear it is NOT the most comfortable pack I've ever worn. After less than two miles I am ready to take it off. It can certainly hold an awful lot: Kodak Master View 8x10, 240 and 360 Caltars in Copal 3, 165 Super Angulon, half dozen holders, meters, with room to spare, and sensible place for the tripod. But again, when fully loaded, it's a pain. I am contemplating two handcases, one for the camera, another for the lenses, meters. Then wear the tripod and holders on my back. No hands free for serious climbing, but looking at my portfolio, I realized I never really did that anyway.
Neal