One very important UL concept to keep in mind when thinking about a sleep set-ups, especially for cold weather, is that your insulating layers — such as hooded down coat and shell pants or down pants — can and should be used as part of your sleep system.
The simple concept for UL is that if you're not using everything you brought, you brought too much; this applies to your sleeping gear as well. Too often overlooked is the fact that by buying a larger quilt, you can augment your quilt's (and pad's) R rating with clothing you're already carrying.
Last winter I did a bunch of experimentation to find the lightest combination with which I could sleep quite comfortably around 0°F. Very long story short, I ended up with a +20°F Enigma, 1/4"CCF pad and a torso/wide NeoAir Trekker air mat, with a total weight of 2.82lb. I got the Enigma in long/wide so there would be no issues at all wearing my hooded down jacket and down pants while using it. My pack goes under the legs/CCF pad for a little more insulation.
This worked for me down to -6°F — totally comfortable. The colder it gets the more personal it becomes regards to what works for you individually, but the multi-use concept remains. You just have to be willing and able to experiment.