I have run Shoei Troy Lee designs for the past decade. They are M rated. The main difference between M and SA is the SA has fire resistant materials. Also the SA has less view area. I am not overly concerned about the fire part, since all of the events that I run have great race rescue. I do have a camlock 5-pt, so escape is fairly easy, unless it is a drivers side impact. I probably will upgrade to a SA helmet after mine expires. As far as impact or strength difference, they are very similar, so those who are now scared that their cycle helmet is not as "safe" it just means that in a fire, it will not protect you as long. That is where the "liability" is raised by HPDE events. It is the "fire" risk.
Thank you... finally someone mentioned this.