I have the Jam2. 30 pounds is doable, at least from the packs perspective as long as you don't strain it. I think ultralight packs should be higher in volume, so you don't have to strain them or use compression sacks, but you have to have the discipline not to bring extra stuff. It really should have a different name, like DontJam2Much. lol
I load my Jam2 blue foam pad in first, tube like, which makes it very solid and consistent regardless of how you carry the rest, but this does use up to 25% of the volume with a 72"x28"x0.375" pad. You can use the pack as a pad extender, and go narrower, and take up less volume that way and still get good suspension. The side straps I use to only just take up the slack, or if I happen to carry something long in the side pouches or across the top and down the sides temporarily. The extra volume of the Pinnacle would have been nice for extra layers and food in winter but I get by with the Jam2 by keeping a medium/heavy wool sweater and 200wt fleece pants on, removing the more packable shell layers, hat and mitts, skin layers, and even blousing up the fleece pants when I am active on warmer days. I would definitely recommend the Pinnacle though, for more volume, even though I haven't tried it. The Jam2 is a nice tall skinny fit for cross-country skiing though. It is sort of like a fastpacking pack for winter skiing, a regular pack for Spring/Fall, and a large pack for Summer trips with daughter. Perfect for me. <img src="/forums/images/graemlins/smile.gif" alt="" />
As far the comfort and durability of the pack animal is concerned, I think 30 pounds can be as comfortable with this pack as any other if you load it with the blue tube method, or some similar way that make it rigid, and then fit it in such a way that at least half the load is on your hips. This is easier when you are skinny because you will lean forward slightly with a 30 pound pack. At my current weight I already have a built in 40 pound frontpack, so I have to rely more on tightening the waist belt to keep most of the backpack weight on the hips. 20 pounds is alot easier than 30 pounds, but even with 15 pounds on hips and 15 pounds on shoulders the blue tube method gives you alot of back support. You have to buy a size that fits though. This one fits me.
p.s. This is not realted to the original post, but I thought I would throw it in...
I would say 30 pounds is doable, but it depends more on the hiker than on the pack. I think even young fit adults shouldn't carry too much, and if you are overweight you should carry less. I think pack weight should be a function of lean body weight, or height, not total body weight. You have to carry less when you are overweight, not less. I'm a big guy at 6', but 30 pounds skin out is it for me when I am weighing 230 pounds, but I could push it with a 30 pound pack weight starting out. When I weigh 30 pounds less I can probably carry at least 15 pounds more, perhaps 20 pounds, not that I would. I do enough extra damage carrying my daughter now and then. It depends on whether your weak point is you back or your knees and ankles. Eventually, for everyone, it will be both. I would recommend people carry no more than their height squared, and reduce this when if they are either overweight or thin boned. So for someone 5' tall, 25 pounds. For someone 6' tall, 36 pounds. Try to reduce it by 5 pounds for every 15 pounds you are overweight. Of course if you are 60 pounds overweight as I am, this doesn't leave me much, but 16 pounds packweight is doable, and a great way to be able to keep hiking to lose weight.