A big factor will be how tall/wide you are. I was seriously looking at the USMSS but it's just not big enough for me ( 6'5'' & 48 chest ) and although they did do a long version of it , I could'nt find one anywhere, and finding new unissued here was very difficult. In searching about I came across the Carinthia and now have a Defence 4 and Tropen, both in the 200 size and they are fantastic bits of kit, individually and combined. I got the Tropen in sand colour just to be able to differentiate them when combined. I also have a flecktarn goretex bivi bag from Germany, modelled after the USMSS one but bigger, to complete the system. Having had a succession of disappointments of sleeping bags over the years I love these things! Some people don't like the fact that the Defence 4 has a small face opening, but this is great for when it's really cold and in warmer times I have simply pulled the whole hood back and under whatever I'm using for a pillow.