I've done a ton of research on different helmets and decided to go with the Vantage because of the vents and removable ear pieces. And because of how light it is. I can't find a local (Houston, TX) shop that carries this particular helmet so I have no way of trying one on. My head is 54cm so by the Smith sizing chart I would need a small (51-55cm). My question is, how do they fit and should I buy the medium since I'm right on the edge between small and medium? Any help would be greatly appreciated.