i was told to run reg. when i bought it off the importer, used it not by choice though, the caltex fuel refinery burnt down just before christmas so reg is all you could get where i am.
the ron is the fuels resistance to explode (so you can get higher compression)
the stagea has a knock sensor which detects knock (premature fuel detonation) and then retards the ignition timing. retarding the ignition timing reduces the tendency to detonate, but also reduces power output and fuel efficiency. so it shouldn't matter if you run a lower grade (i think, correct me if im wrong) you'll just get really really bad fuel efficiency