I've used external frames, internal frames, and frameless packs. When I started out more than 50 years ago external frames were everywhere. (I don't think internal frames had even been invented, yet, though I could be wrong.) I transitioned to frameless packs sometime in the mid to late 70s after seeing how much better they typically performed off-trail and, especially, after I took up cross-country skiing. As for frameless packs, I have only used a 20(?)-litre one as a day pack or for over-nighters. I've run into people on PCT going ultralight--under 15 pounds--it's not for me. I typically use one of my 35 to 50 litre packs, carrying about 20-25 pounds (pack, pad/bag/bivy/tarp or tent--too many different configurations to list, and a very few supplies) + food and water. Size really depends on how much food and water I have needed to pack and the season for extra clothes. (These are not big packs by backpacking standards: How to Choose a Backpack - REI Expert Advice - REI Expert Advice) I did try a 70-litre military rucksack for winter camping once. (I hiked into the Deams Wilderness in the Hoosier National Forest for a week long trip where I had to pack all my food and winter gear.) That was a strain, so I switched to pulling a pulk for a few winter camps in the wilderness, though I'm too old for it now. In fact, I feel like I'm getting too old for hauling much of anything, on my back or through my hips, hence a bike!

BTW, glad to hear steep roads are not a problem in Colorado, maybe I'll push on to Utah and do some more gem prospecting! ;-)