Take a look at the backpacks in the pictures. Both packs are empty, but the red one, with external frame, is already twice as heavy as the green one. And, because it is much bigger, you will cram extra stuff into it.
The red pack is almost identical to the one I used on the Appalachian Trail in ’03, and it topped out around 47 pounds (including food, but not water). I don’t think I ever got it under 40 pounds, and this contributed to a knee problem I had out there.
I learned the hard way to buy a light pack and to pack light. I used the smaller, no-frame pack on the Pacific Crest Trail and topped it out at 31 pounds. I doubt my knees would survive the A.T. today carrying over 40 pounds plus water. Today you will find ultra-lite long-distance hikers who carry less than 20 pounds!
Ray Jardine was the early guru of light backpacking. I studied his 1999 book Beyond Backpacking and learned a lot. And I’m going to buy his new one, Trail Life: Ray Jardine’s Lightweight Backpacking. Reducing pack weight is the number one issue for any long-distance hiker. If it isn’t a necessity, don’t haul it. Modify what you have. Rather than the old Boy Scout metal fork and spoon, buy a plastic spork. Think tarp rather than tent in milder weather. Get a tiny stove. Do you absolutely need a stove?
What a difference a light pack makes!