You may want to look into Nutnfancy's older backpacking videos and gear reviews. Probably the models discontinued but the principles could be applied to packs today. He was a big proponent of external frame for larger packs. He's the only other person I've ever heard talk about carrying 100 lbs in a backpack before: https://www.youtube.com/watch?v=ynIlrp3r_zY&list=PLogYo97B9UOfDaqOIdI0d9IYLAGoSHdl_&index=3