I tried on this pack today at the local outfiter (the pack is great) He only had a large. I measured my back and according to the osprey website, I should wear a large, but just barely. I think I made the the large by an inch or two.
The fitting problem comes with the waist belt. I added weight to the pack and cinched the waist belt as tight as it could go. However, even with all the slacked cinched in, the wasitbelt wasn't super tight. I know I will lose weight on my trip and I like having a tighter waistbelt. Does this mean I should go w/ the medium???
I also picked up the Montrail Masai's They are awesome. Light, comfortable and tough.