The 91 and 95 for the different fuel in Thailand are for the Octane rating of the fuel. Octane is a measure of gasoline's or gasohol's resistance to self-ignite during the compression stroke, see more at Octane Rating at the Pump.
The E10, E20 and E85 are a measure of how much ethanol is used in the fuel. For example E10 is a fuel mixture of 10% anhydrous ethanol and 90% gasoline, E20, is a fuel mixture of 20% anhydrous ethanol and 80% gasoline and E85 is a fuel mixture of 85% anhydrous ethanol and 15% gasoline.
The regular fuel (gasohol) we buy is rated as E10, 10% ethanol and 90% gasoline.
The problem is that ethanol has a different burn rate as gasoline, so the more ethanol in the fuel the more the fueling and ignition of the engine has to be adjusted to give the optimum performance.
With the Flex-Fuel on the Yamaha Fino 125 you can fill up 2 liters E85, and 1 liter of E20 and a liter of E10 fuel and the engine will still perform the same. But Yamaha advice owners to use RON91 fuel for the Fino 125.
Ethanol has a lower energy density so to get the same power you need to use more fuel. Sometimes as much as 25% or more.
E85 has 33% less energy content than 100% gasoline (and 30% less than the E10 gasohol blend
So owners will have to do their own testing to discover which fuel is the most bang for the buck , so to speak.
But E85 has the potential for producing more HP if the engine is tuned properly. Up to 20% maybe. As the Fino is probably the most modified scooter I am sure the aftermarket parts will follow. There is already an E85 PCX kit with something like 14:1 compression . For competition of course