[JOHNSONROD]

i think the big point is where you are allowed to use them. we can compare stats all day and its fun to bench race and hear different opinions. the thing is if they wont allow you on track in an M helmet, just get an SA and be done with it. i dont know all the specific differences for a fact, ive always heard it was the multiple hits and fire protection.
i think the only time we allow an M helmet on track is in a lead follow format where speeds are controlled by a pace car. the SA 2010 minimum is mandated by the track and is not optional by the club renting the track. other tracks may have different rules. ours is very strict about safety, mainly for insurance and liability reasons.