Honestly, you need to find the helmets locally and try them on, then find the best price online and order them, or get a local place to match them.
Personally I don't really like ordering a helmet online cause I find the postal service pathetic at the best of times, and really don't trust it to arrive in pristine condition (internally even if it looks fine otherwise).
I got my shoei from the helmet warehouse in sydney, was very pricey but worth it.