I'm still using the "ridgerest inside, mylar outside" technique and have been warm enough to have been 'iced in' once and never knew it....until I peeled myself out in the morning. In this part of the country we don't see temperatures like you describe, maybe 25 deg. My goal is to trade the ridgerest weight for an underquilt of the same weight and elliminate the pad. Of course, that pad is my pack frame...hmmmmm.