I currently use a mummy 600fill down sleeping bag rated for 20*. I was thinking of purchasing a Big Agnes sleeping bag, which saves weight by eliminating all insulation on the bottom of the bag (which when crushed by the weight of your body is useless anyways), and allowing you to spend the ounces on real ground insulation, like more thickness in your sleeping pad. Other companies taking this a step further just sell down blankets, with cinch-cords on the bottom to cup your feet. They weigh almost half the weight of comparable mummy bags, (usally a pound less) which you can use to add an extra inch of thickness to your thermarest, or just save weight when hiking in warm weather. I'm thinkning of an 800fill down blanket with 4 inches of loft. This would effectively be a 0* insulation barrier for just under 2 pounds. Along with a nice 2" thick full length 2.25 pound thermarest (rated for 0* as well), you would have a 4-season sleeping system with much more versatility and comfort than a mummy bag and 3/4" Thermarest (which I use now). Your thoughts on this...