X2 on Mr. Steve O's comments (LOL)!!!
I used a Eberlestock Blue Widow on a Alaska hunt. Overall a good pack, but once the weights exceed 40-50lbs, it was brutal (at least for me). Summer before my hunt I trained by mowing the lawn, and walking with 50lbs of rocksalt in my Eberlestock. I was sore all summer! I figured it was just me, until I borrowed a friends Sitka45 pack. No issues with back or shoulders with 50lbs of rocksalt in that pack. After I realized, my issues were more with the pack then me, I began my search for a new pack.
I really liked the comfort of the Sitka45, but I wanted more cubic inches, plus the Sitka pack is "too busy", pockets everywhere!!
I ended up buying a Kifaru Timberline 5200. WOW! Night and day difference in quality from the Eberlestock (buckles, straps, stitching, material etc.)Plus, I can add pockets, pods, pouches etc. to the Kifaru. Took the Kifaru on a elk hunt fall of 2012, very comfortable with 50lbs inside. Plus it compresses nicely as a daypack on a extended backcounrty hunt.
I have no experience with MR, but I stayed away b/c of there overall pack weight. I am sure they are good packs.
My two cents......
chris <><