I continue to be impressed by how much these Stone Glacier packs compress down. I've seen the 5100, the 7400, and the Solo in person and man are they light and tight packs.
Thanks for the insightful discussion. Hunting season is usually either pouring rain or snowing. And I find that my bt1 is perfect for packing in all the gear I need to set up camp and hunt from there for 8-9 days. But scouting trips are shorter: 3 nights on average. So I just don't need that much gear, food, etc. and would like a smaller pack. Also, I'd like to do more backpacking. With an ultralight pack, I can bring the pack and cook and sleep systems to weigh less than the bt1 alone. I don't see any need to carry extra weight unless it's strictly useful, so I'd rather find a comfortable light pack, something not as rigid as the bikini.
So far I have purchased and returned: a gossamer gear mariposa, six moons designs 60 pack (can't remember the name), ULA Ohm 2.0. Of these, the Ohm carried the best and was for me the most comfortable. It's also the smallest. I'm having ULA make a larger one out of cuben.