Have you ever thought about/looked into getting a real hiking backpack, and adapting it to hold camera gear? Kind of like approaching the problem from the other end.
The problem I have with most photo backpacks is that they have not a lot of room or convenience for anything that is not a camera or a lens, and also they tend to be pretty heavy for what they carry, due to the huge amount of padding they have. Hiking backpacks are a lot lighter and usually seem to have a much better fit. IMO, a properly fitting and comfortable backpack is of extreme importance when you go out hiking. There may be a great camera bag that holds all your stuff real nice but if it is not comfortable to wear and adjust, then it is going to be a long hike no matter what.
I have been using the Osprey Stratos 24 for my hiking. It's extraordinarily comfortable and it has some airy back feature that REALLY helps with staying cool when hiking in the summer. I picked it out amongst many hiking backpacks specifically due to two large straps that go across the back which can be used to strap in a tripod, however, I found through usage that it is better for me to strap it in the side pocket rather than in the middle on the back. I found that even though the weight is centered, it is very far away from your back and thus you feel a constant "pull" that is trying to pull you backwards. Getting that tripod weight closer to my back made it a lot more comfortable despite the fact that it is off center. It sits really securely on my back and does not shift around at all, so I do not have stability/balance problems from it. BTW I have a 2-series Gitzo CF which weighs about 4lbs including the ballhead.
The stratos 24 also has mesh pockets on the hip belt which were really handy for things like filters, or spare batteries/memory cards, etc. I bought a LowePro lens case that I can strap onto the shoulder strap of the backpack and that gives me easy access to a spare lens without having to stop and take off the bag. If you need more room they make a larger 40L version with the same basic design features. I nearly bought it last summer when it was on sale but resisted.
Anyway, my point is, perhaps have a look at some real hiking backpacks and then look into Domke. They make these inserts which can be mixed and matched to make your own insert to hold camera gear. They also make these squares of neoprene with velcro on the corners which can be used to wrap camera gear (i.e. wrap a lens) that can then be stuffed into the bag in any fashion. The way I see it, with these photo backpacks you need to stop and take your bag off to access the gear inside anyways, so it's not that much different than stopping and taking gear out of a standard backpack. You may get a little more flexibility by going this route, and also you can use the backpack for uses other than photography (even though I found now that anytime I am out hiking, I am bringing my camera along anyways). It's a big job to sort through the available backpacks and coming up with a good scheme, but I believe that once you find a good setup that works for you, the real backpack + inserts route is going to be better than a "photo backpack"
Ruahrc
