I actually wore my Icebreaker quarter zip when I commuted to work Wednesday. It was 42 out at 5:30 AM. It might have been a bit too warm with a LS Craft base layer and a wind jacket, but my regular jerseys are too cool for that temperature and my other 2 wool cycling specific jerseys are way too warm for that temperature.
I keep thinking "this is the last time I will be wearing my Shak for a few months," and then we have another raw, cool day where it is the perfect thing to wear. But I am trying to stay away from any purchases of wool for a few months. Of course, if anyone sees a black full zip Shak in an x small, tell me!