I was able to stop in at the San Mateo Motorcycle show during my travels this past week and I tried on the C3.
I own both a C2 and S1 in size XL. The fit is consistent between the two and both fit me well. With the C3, the XL was too big. I felt like I was swimming in it compared to my current helmets. The C3 L fit OK, a bit snug, but I suppose it would loosen up. I liked the helmet overall and will consider it when I need a replacement.