Don't omit the Six Moon Designs packs when you're researching. I have their Comet, a now discontinued "little brother" of their Starlite. With the "optional" (mandatory, IMHO) aluminum stays, it comfortably carries up to 35 lbs. or a little more. I especially love the load lifters because my shoulders are extremely pressure-sensitive (more old age...).

The pack for you is the one that fits you (pack fit is almost as individual as shoe fit) and comfortably carries the load you want to carry. The latter is the reason for getting the rest of your gear first (including the weight/bulk equivalent of a week's food). Carry it around the store or your house for several hours, fully loaded, before taking it on any trips.