Did you have to round the back to counter the weight or were you more upright?
With I estimate about 80% of the load supported by ones hips, I'm pretty much upright going level or downhill, but have some forward lean when climbing. Again, I use external aluminum tubbing frames with no bag or bottom shelf. Give me about 12 feet of line, and I can lash anything on such that there will be no movement.
My initial frame came from a backpacker, and did have a bag. That was removed and left in the wilderness on my first encounter with an elk quarter. The bag would have forced a high position load and was not roomy enough for quarters carrying ribs. I now have 3 identical frames that are 1970's Sierras. Not had need yet, but always figured it best to have backups. All have a tight mesh webbing lashed from top to near bottom between the uprights that keep the load about 1 1/2 inches off of ones back. Excellent for evaporative cooling. Heaviest loads to date were moose hams and shoulders. Took a little help to get upright with those.
From observing others, I have no desire for the body hugging flexible plastic units. Not sure they would hold up in subzero conditions either.
Not looking forward to packing a bison though.
