I did 26.2 in Ann Arbor MI in March one year; 16F when I started, 26F when I finished. The course was all asphalt but it was quite hilly slowed me down.

I wore knee-length running capris. I did wear layers on top. It was very windy, and I froze, but there would have been no avoiding that in the wind even with tights. I wore 3 layers on top: a short sleeve tech shirt under a long sleeve shirt and a cold-weather running jacket. Gloves. Headband. Because of the wind I was uncomfortable the entire time, but only from the waist up; my legs never bothered me.

If I were to do that course again under similar conditions I would have more upper layers but I would still wear the knee length capris. They were actually pretty thin. On the other hand if I knew it was going to rain or snow I would go for the tights. Being wet on top of that wind would have killed me.