For too hot for headcovering and too cold for bare ears days I wear a full shell "urban" helmet and a earband. The urban helmet has rear vents and air space above the head so it "breathes" that way.

Another way to look at this: you sweat in the summer and have wet hair when riding hard, why are you concerned that you do the same in the winter **IF** you have something that doesn't stop being somewhat insulating when it get hits with sweat?