Not really hijacking the thread, because it's relevant to the author's question, sort of
But, there has been a great debate in the Moto community re. the validity of the Snell M standards as compared to ECE or DOT ones.
While I don't think there is a better existing standard for Automotive or Track helmets than Snell, their Moto standard seems a bit wanting. I have worn an ECE 22.05 rated lid for a few years and will continue to do so.
It'll be interesting to see if any of the modified Moto criteria for the M2010 rating will spill over to the upcoming SA2010 (Automotive) rating. If interested, you can read more here:
http://www.motorcyclistonline.com/gearbox/motorcycle_helmet_review/.