I didn't see this thread when it first came out--was out of town.

My own experience with external vs. internal frame is that the external frame that I used for years kept pulling me off balance--it inevitably zigged when I zagged. My first trial of an internal frame pack was a revelation--it moves with me instead of against me! Your mileage, of course, may vary, but I suggest you try on several models of each, with a load, before deciding..

Be sure to try any new pack with a load, preferably the gear (plus the equivalent in bulk and weight of food and water) you plan to carry in it! Do a lot of twisting and turning and going up and down stairs. When you get it home, immediately do a several hours' "hike" in the house or (if nice weather) around the neighborhood, being sure to keep the pack clean (and leaving the tags on) so you can return it if it doesn't work for you. Pack fit is almost as individual as shoe fit!