Originally Posted by Rafgar
As you see from Dave's reply, there are some very definite opinions on what you should use for safety equipment. I'm not arguing with Dave (and yes, I have an SA rated helmet). However, the current minimum requirement for participation in NCC schools and autox is for either an SA 95 or an M 95 rated helmet.
As was mentioned in a previous reply, your best bet is to spend some time at OG Racing trying on different helmets to see what fits. If you're concerned about the initial investment, they rent helmets.