Brian in OH wrote an answer about MontBell U.L. Super Stretch Down EXP Hugger Sleeping Bag: -20 Degree Down on May 15, 2008
i've tried this up at the arctic circle. it worked fine with its -29C rate. The rep is wrong. This sleeping bag at -40C would feel chilly, but it really depends on your metabolism. For me, -32C was the limit with this bag. Right now, I'm contemplating whether to buy another one or get a Marmot Col EQ.