If I could just chime in here, if you go down to your local shop and spend twenty minutes with their helmet guy figuring out what size you wear in the model you like, and then you say "thanks, lemme think about it", he'll know what you're up to, he will hate you, and he will remember you on that last nice weekend of the year when you really, really need a new drain plug because you lost yours in the middle of an oil change.
Just a heads up.