I think the -20/USGI advice is sound. My lighter bag is the one I'd carry (because I'm not hiking when it is that cold). The cold weather bag I'm looking for need only be carried 50' from the Jeep to the tent, so weight is not a factor. Bulk either, since I don't take the whole brood with me in low temps. I'm gonna go to the surplus store on Broadway and Hampden and see what they have.