Being the Gear Freak that I am, I went and ordered a Jam2 from Prolite. They didn't have a large so I went with a Medium, even though, most say to size up. I do favor backpacks, almost to the same degree as Franco with his Tarptent's? HA
I think, my current count is 8 packs, excluding 2 day/hyd. packs.
I did see Will R. review on the Jam, and in the first picture, it seems that the pack is actually too tall for him, with the shoulder straps almost level with the top of his shoulders.
I personally have found that a good wrap over, is a better or a more equal balance for load carry. Instead of trying to carry more of the weight on the hips.