Timwrote a review of Western Mountaineering Puma Gore WS Sleeping Bag: -25 Degree Down on January 2, 2016
Have had my Puma GWS down to -20*F and stayed nice and warm, especially in the torso/head region. Have never used a dedicated winter mat. However, with a good high R-value mat this guy should be good down to minus thirty, no prob. I use a size Large S to S compression stuff as long as you stuff the bag inside out!