I have been using a Marmot Pinnacle 800 fill down sleeping bag rated for 15 degrees. It was the biggest bang for the buck rated at 10F degrees for men and being 800 fill is quite compressible compared with a simial 0 degree bag with 650 down. I was actually worried that a 0 or sub zero bag would be too warm (note one should seldom worry about being too warm in sub zero temps. I know that now )The first night I tested it was -8F and combined with the HH SS ocp pag and a space blanket I was very comfortable. SOMETHING TO THINK about: where I live near Lake Michigan the relative humidity is quite high. it is 19 degrees right now with the humidity at almost 90%. However where I went camping the Humidty was down near the low 50 range, much drier. Considering that the dew point is in the single digits, I am curious how that may effect temp ratings in camp gear.