I stumbled across this thread and though I would add some information...
M rated helmets are tested for single impact. SA rated helmets are tested for multiple impacts. Many M rated helemts do not come with fire retardant material on the inside of the helmet. SA rated helmets are tested and are designed to contain fire resistant materials...
This will explain more about the differences in rating and why the SA are priced higher... http://www.smf.org/
We almost always recommend a SA rated helmet. Why? It covers all the bases. A customer can go from Autocross to track days and beyond with SA rated helmet.
We offer both M rated and SA rated helmets. SA out sells M rated two to one for us. We don't even advertise the M rated helmets any more.
We prefer Bell/Pyrotect. We think they offer a great helmet at a good price. Other brands are just as good... As long as they are M or SA rated.
Open face/closed face is a preference. I use the same exact helmet as Big Sky. It is actually a rally helmet.
If we can help in any way, please feel free to email us at JnJAssoc@aol.com