If you are very snug in the Large RX-Q that probably puts you at about a 60cm head size, the C3's sizing is slightly small, with the L topping out at 59. You would probably be on the small end of an XL C3.
I would start there.
Originally Posted by dfsavgny
I wear a large in the Arai RX-Q (a little snug but okay). Would a large in the C3 be comparable?