Well, no one has mentioned it but for about $30 you can get an alice pack and frame, which is pretty bombproof as far as packs go.
This is an interesting video which suggests that the Large ALICE pack sucks. (not my words)
http://www.youtube.com/watch?v=FBakphJvNIsIf your going to be carrying more than 25-30 pounds I would avoid the Large ALICE pack like the plague. There are packs out there with modern adjustable suspension harness systems (such as catering for back height) which transfers the load to the hips i.e. such as the military packs from Lowe Alpine i.e. the Lowe Alpine Salient.
http://www.youtube.com/watch?v=GkT2Rfggq5k