I just got back from Crested Butte, CO where I was hiking with my Ape Case 2000. I had my 1D2 mounted with my Sigma 50-500, my 1Ds2 mounted with my 24-105, my 17-40, my Sigam 150mm Macro, my 580ex ii, all my cleaning stuff, remote triggers, etc. I spent several hours at a time hiking the area and my pack was very comfortable. It is very well padded and it holds a lot of gear. Oh yeah, there is ever room for a 17 inch laptop, but I don't use that area for anything.
Not sure how much you hike or how difficult your hikes are, but I spent 4 days over 10,000 feet above sea level and I had no issues at all. If you know how to properly wear a pack it will be comfortable. It is my personal experience, with photographers AND hikers, most that complain about their pack are the ones that were not properly fitted. Either they have the wrong size pack for their torso or they are not wearing it correctly. If you hike a lot, then you know what I am talking about...those goofballs with their packs riding high up on their shoulders. LOL I have a long torso so the Ape Case 2000 fits be perfectly. If you have a shorter torso, it may not work so well for you. It is all about the fitting, get a proper fitting pack for your torso and you will hardly even feel it.