I carried a Deuter ACT Lite 65+10 on my backpacking trip. It has three large external pockets, two hip-belt pockets, and internal and external pocket on the lid, and the main cavity is divided into a sleeping-bag compartment at the bottom (accessible via a separate zipper) and the main compartment on the top. The two compartments can be combined by zipping away the divider between them. Mine weighs 3.8 lbs. and it’s red.
The separate (and separately accessible) sleeping bag compartment is a godsend, partly because it’s actually big enough to hold both my sleeping bag, and my tent (both in compression sacks). My pad is strapped on the bottom of the pack, so I can pull out everything I need to have setup camp in less than a minute. Note that the pack doesn’t have its own straps for attaching a pad; I had to MacGuyver some on to it.
The nice thing about the separate zipper for the sleeping bag compartment at the base is that it allows equal access to both the top and the bottom of the main compartment, while providing a bit of organizational structure. In packing a backpack, there are two semi-contradictory goals:
Pack things in the reverse order in which you will need them. E.g., you want to pack your tent and sleeping bag inside, so that things like snacks, lunch, maybe extra clothes, are neat the outside, readily accesible while you are hiking.
Pack heavier items towards the middle of the body of the pack, close to your back so that they are close to your center of gravity.
With just a top-loader, you are essentially constrained to either optimizing for accessibility, or for hiking comfort. A separate zipper (or a panel-loader style pack) gives more flexibility.
Extending the extension collar adds another 10L to the volume of the main compartment, something I needed after my gear “expanded” after being re-packed the second day. (You should never pack your pack to its fullest capacity; expect your gear to “grow” by about 10% after the first night.)
Comfort-wise, I had no trouble. My left shoulder became a little sore, but I suspect that’s because I carried my camera (attached to a Peak Design Capture) on the left shoulder strap. My load was about 30 lbs. and the Deuter gave me no problems with stability or the pack moving around as I walked.
Bear canister placement was a bit tricky. I was using a BV450, which doesn’t quite fit when right-side-up, but fits just fine horizontally. It does, however, leave a fair bit of empty space to the sides of it, to be filled with stuff sacks or dirty clothes or whatever was at hand.
The side pockets are relatively easy to access while walking; I kept a water bottle in one (tent poles in the other). The crucial task of putting my water bottle back in the pocket without stopping to take off the pack became easy after a few tries. The side pockets are surprisingly deep; a shorter water bottle would have vanished inside it, as my bag of gorp did.
Although I like my ACT Lite, I should mention that I picked up a 2014 Six Moon Designs Fusion 65 on clearance. It’s much lighter, but lacks the bottom access and separate sleeping bag compartment. I’m anxious to give it a try.