I run a MR Pintler for my pack for the same reasons you mentioned(load hauling day pack) and love it. I also have both the Kuiu and AGC Bino packs and like them both although I run the AGC unit more often as it can carry lots of little things I like to have handy including my GPS
One last thing have you thought about getting a gun bearer. Check out the Kifaru gun bearer. Another awesome upgrade to your kit.
There's always this one too