If you're relatively sure you will be cold in a 30*,you could get a 15* and just use it open as a quilt when it's warmer. I agree with the others that FF or WM are exceptional bags, Katabatic also makes great quilts. I own a WM Summerlite, and a Marmot Helium...got a great price on it :-)I also have a hammock and use a 20* top quilt and underquilt. When in a tent though, I find I take the Marmot more often than not because I'm a very cold sleeper. I also do most of my backpacking trips in cool to cold weather (live in the south)or in summer at elev. that tend to be cool at night. YMMV. Good luck.