On the coldest day this month, started before light. Well, it must have been below freezing because I saw frost on the back end of cars. ( Needed good light to look out for black ice.) Wore fleece lined bike tights, UnderArmour tee shirt.glove liner and winter gloves. Thermal lined bike underwear. I was pretty comfortable. Except could have used a backlava.
BUt, I think the most helpful was lycra shoe covers.