For one of my fillings, I filled her completely up with 87 USA Octane, which is about 92 RON.
We spent the night at a mountain hotel that was a touch over 10,000 feet elevation, 3050 meters. The next morning, the bike (which is brand new), had difficulty starting. My next fill was with 91 USA Octane (95 RON) and she ran perfect.
Here in Colorado 91 USA Octane is the highest rating at most pumps. But I understand that has something to do with elevation. In other words.... supposedly, 91 in Colorado is equal to 94-95 at sea level.