Race gas has a couple of advantages over pump fuel. First is consistency. Pump gas, even from the same pump can be highly variable. Second is race gas usually has no alcohol in it. This means less water absorption which tends to displace the oil in premix but also no waxy build up in the fuel system as the alcohol breaks down.
As for the octane needed to prevent pre-ignition that is solely dependent on the compression ratio. There will be an optimum mixture for a certain compression and ignition timing and bikes with similar compression ratios will have similar octane requirements. You can reduce that requirement with an accessory chamber from S3 as I did on my '13 EVO. I still run race gas though because I like the bike to run consistent a I'd prefer to disassemble and clean the carb less than I have to with pump gas. As for years of EVO I ride with guys that have an '11, '13, '14 factory and a '15 factory. They all have slight differences but are pretty similar in form and function. Biggest difference is in how the bikes have been treated. Beat bikes will have more issues than Sr ridden bikes.