cocadori,

I will second the suggestion of an external frame.I still have my Kelty from the 60s and still use it occasionally.

I once took my whole working bag (about 35 lbs. at that time) over the top of Kathadin along with my regular backpacking gear (also about 35 lbs. at that time), and had no trouble handling the load.

Incidentally, I met Ed Garvey on the top of Kathadin that trip, and took the picture that became the cover of his book. That experience is what inspired me 25 years later to do a thru hike myself.

In case you're trying to compare, the load was three Nikon F bodies, two motors, five lenses, flash guns, meter, and odds and sods. I was working for UPI at the time and shooting company transparency color film.

best, jcp