I have a large mens Go-Lite Jam2. I like it alot, even for short winter ski trips, but I think the Pinnacle would be better for longer winter trips though I've never had the chance to try one on. Here are some comments on the Jam2...
When I pack it my 72"x28" blue foam pad goes in first, like a cylinder. This takes up 25% of the 3200ci, but it carries very well this way, and is nice to sit on. Sleeping bag and bivy sac go in next, then food bag, then spare clothing, then a small rectangular ziploc box that contains miscellaneous items and keeps the top of the blue foam rectangular. Then something to keep the rain out, like a plasticized map, or stuff sac. On the downside the back pouch does not have much room left when the main bag is stuffed rigid with the blue foam pad. The Jam2 is waterproof, which is generally a good thing, but I wonder on a very wet trip if it might be better if it was breathable. I might replace the back pouch with a more expandable mesh pouch, for wet clothes, and my Kelly Kettle. The side pouches and straps hold water bottles up to a fairly large diameter and whatever height you desire. I'm looking to nest a couple of pot/mugs there with the bottles once I find the right diameter, and perhaps a hobostove.
Weight shouldn't be an issue with the Jam2, as long as you use the blue foam cylinder method. Volume might be an issue. Not sure about the Pinnacle, but it looks similar, only bigger. To save volume you can cut the pad short and use the pack and its pad for your lower legs. You could go with a narrower pad also, which effects the height of the cylinder if you want to reduce volume in summer or for day hikes. I have tried using the Jam2 as a bivy for my legs, thinking I could cut my gortex bivy down to a rain cape, but the Jam2 gets too narrow at the top to fit my upper thighs with a sleeping bag. The Pinnacle might be roomier. The other thing I could do is cut the Jam2 and add a stretchy panel, but I don't want to mess with it too much. It is good at what it is, which is a good intermediate sized pack big enough for long summer trips, skinny enough for cross country skiing, and still small and light enough for day hikes. Very versatile pack, but somewhat inflexible in places.