Great write up and summary. I used the Gunbearer this year and loved it with the exeption of steep climbs. I found myself strapping my gun in the carry pocket of the pack in these situations.
I've been using the Tenzing BV16 for 2 years now. Very comfortable and good organization. It has held up great in the thick grouse woods.
https://www.tenzingoutdoors.com/catalog/product/view/id/489/s/tz-bv16/category/111/
Checkout Ammoseek.com, great source for finding what's available.
Also, I'd consider the .308, much better ammo availability and plenty of "knockdown" for elk.