I have used a 20 degree EE quilt for all of my trips over the last couple years in Arkansas/Tennessee, but would like a sleeping bag for colder temperatures. I found that the Enigma is best above 30 degrees and becomes a pain in the low twenties, and that one time in single digits/teens only gave me 5 hours of sleep. I am 6'2 220 side sleeper with a 50+ inch chest which is why I have never owned a sleeping bag. I am looking at the Nemo Sonic line of bags due to their width and can't decide between a 15 or a zero degree bag. This will be my only sleeping bag and I will use my quilt on all trips with expected temperatures above the high twenties. Considerations are that I want this to be a long term investment and I am in the military/will be stationed in different climates. I like the idea of the vents on the zero and that bag would give me two sleep systems to cover all temperature ranges, my concern is that it may be too warm in the 25 degree temperature average of Arkansas winter over the next month or two.

The 15 degree would work best for me at the moment, but I feel as if it overlaps with my quilts temperature range and am interested in future winter backpacking down to zero degrees. I've read that the sonic zero isn't the warmest zero degree bag, but I don't plan on camping in temperatures that would require dedicated 4 season tent/boots/etc.. I tend to push the comfort/safety boundaries on clothing and always hike alone if that's also something to consider. After suffering through the recent cold front that brought single digit temperatures in my 20 degree quilt I am okay with carrying an overkill bag for temperatures below freezing for a pound weight penalty. I already own a larger volume frameless pack, pyramid shelter, and adequate clothing for single digit temperatures.