Thanks for the replies, although I'm still a bit mystified. I don't think my hands or feet have ever gotten uncomfortably cold while I was doing strenuous exercise, unless they were wet. I've never biked in the winter, so maybe that's different somehow.

Would adding more core layer insulation help? My friend tells me he dresses pretty lightly overall, I think because he doesn't want to sweat too much. If he's going to sweat anyway, no matter how lightly dressed he is, does it matter if another layer makes him even warmer?

David