Stone glacier has a line of military packs. Check them out.
Sounds like you could use a sherpa??K4 all the way. One thing I noticed was a game changer during packout of two bulls and a cow elk this year was that when packing meat/quarters in the load shelf it has its own stabilization/cinch straps separate from the pack portion and the system is simple. So when you buckle your pack down on top of your meat load you don't lose the functionality of your pack accessibility or anything strapped to it like your rifle/tripod AND it significantly stabilizes the load to prevent shifting weight. If that makes sense. Also I ran kuiu for a few years and did a heavy packout (100+lbs) of a bighorn sheep around 20 miles out of the frank. At one point we traded packs so I could see how my buddy's k4 felt loaded down. Came home and sold my pack immediately. I don't know which was worse…how much better his felt or how miserable it was to put mine back on! K4 handles heavy like a dream. Now heavy pack-outs are fun.