Several rides on the new 58cm CAAD9 convinced me the fit is good and this bike is a keeper, at least for this season.
The medium helmet looks better on my head but just barely fits and there is not enough room for a cap or headband underneath. The large size is really big but it will be fine. Overall it's a comfortable helmet and a cool design and I'm glad we got them.
Some of the Decibel helmets in my garage