M is specifically for motorcycle racing.

SA is "special applications" which translates into auto-racing.

I believe the M90 is out of date.. I think helmets are only good for one generarion back from current. Which happens to now be m2000 or sa2000

I'd say get the new one.

Dave Andrews
Black&Tan 2000 SVT 225 of 2150
Bassani.. UNCORKED
davelandrews@comcast.net
"Nothing is so firmly believed as what we least know." -Montaigne