I know I am in the minority here but I like a big pack. I hunt in PA (coldish winters) and hike in a good piece over elevation changes. I like the idea of putting my outers, as well as multiple base layers, game bags, hydration pouch, food for an all-day sit, binos, saddle, etc inside the 38 pack and getting dressed at or near my stand location. I would theoretically put my RR platform and WE stepps in the overload shelf.
Also... check this out- If you search for "Pop up" on mystery ranch's website a new Mule bag shows up with the Pop ups. It also includes this language in the description: "For those who already have a Guide Light MT™ Frame or a new, 2020 POP UP Frame, the MULE is a 23 L pack sack that attaches to create a workhorse hybrid for multiple hunting applications."
Does this mean I could buy a PU 38 and switch to the bag to the mule if I wanted a smaller pack for a short hunt?? It doesn't mention bag switching anywhere on the Pop up pages for 38 or 28.
That would be a pretty sweet early season setup (mule) to switch later to a rut/ rifle season (38) weather for me.