I'm glad to see that you went with the SA instead of the M.
One of the differences between SA and M is that the M is not fire-resistant (actually, they burn quite nicely whether your head is inside it or not).
Another big difference is that the M is designed for one big hit instead of a lot of smaller ones as you bounce around off things inside your car. Even without a cage, A-pillars, B-pillars, and roof structure won't budge much when a helmet hits them, and you'd probably be amazed to learn just how far the human body can be stretched in an "incident".
Leave on the last yellow.
Norm