I know we are talking races and I have done plenty in the low teens, including a half this year. No problem. The real rugged stuff is Nordic ski racing. Sweat like crazy on the uphills, freeze on downhills. Repeat, repeat, repeat.. and how about Canadian Ski Marathon 100 miles, 50 each of 2 days. I remember well well below zero at the start of day 2. Vaseline on the face. Forgot where knickers met socks...frostbite. 1978 or so.