Oh, heck. 50-60 I'd wear a long-sleeved jersey, the lightest nylon jacket I have, thin wool socks in my normal cycling shoes, knickers, regular fingerless gloves, and a light balaclava
http://www.amazon.com/Turtle-Fur-Fro...ava+turtle+fur
I hate getting my ears cold and this is about the lightest one they make. Sometimes I just wear a headband over the ears.