OP: how long is your commute?
Mine is 15.5 miles each way and in winter when it's below freezing and I'm wearing multiple layers, it always seems like I'm slower. Usually takes 80-85 minutes in the morning. 20F is about my limit. My toes feel frozen after about the first half or so. I'm just not prepared or equipped (nor do I desire) to be out in the cold that long when it's below 20. And really 20 is pushing it. The other morning it was about 24 with a wind chill of 18 and I felt like I barely made it.