It's already been said but I don't think the value of going to REI to have one of their folks talk with you, look at you (torso, hips, posture, expected carry weight, etc.) and then let ypu try out a couple of packs with some weight in it to see what feels right.  I felt kindof like a dork at first but I wandered around the store with a couple of weighted packs on trying to figure put which on felt best AND having the REI folks helpd understand jow to fine tune that pack for me.  

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