Ok, you Aussies and Europeans are just making this confusing
To be clear, in the US and Canada, we use an average of MON and RON (M+R/2), Australia and most of Europe use only RON. MON is taken at higher RPM, so is typically 8-12 points lower than RON. In other words, M+R/2 measurement is usually 4-6 points lower than RON alone.
Our 93 octane is the same as your 97-99 octane 