L5 surgery for me back in ‘91. I am now 61. Last year I did a backpack hunt, 50pds of gear. I use a Mystery Ranch Metcalf. It fits my back and also adds support. Each individual is different. What works for me my not work for you. I would suggest trying on several packs with weight...
Good vid on the difference between the two MR frames. I did not see this posted in any other thread, hope its not a dupe.
https://www.youtube.com/watch?v=x827H-O_LdU