Just an update on the Poncho Liner Underquilt -
I used it last night to hang under the stars and watch the Geminids meteor shower. I nestled down in a 20° Campmor down sleeping bag inside a 15° quallofil bag and the temperature last night got down to 0° fahrenheit here.
I fell asleep after about 40 minutes and 25 meteors; stayed warm and cozy all night long!
It's hard to say how much extra warmth the quallofil added underneath, but the combination of that and the poncho liner underquilt were more than adequate for 0° F!