I sized myself and I was at the bottom of the large scale without my balaclava, so I got a Large and it fits just right. Snug, but comfortable.
I'm not too worried about the small strap. Maybe will drill out the rivet that has the original strap and re-rivet it on the new helmet, but like I said, not a big deal to me. I did spend an hour or two bedazzling my helmet to match the new livery on my car though.