My car takes only 98 RON or better. It's written in my manual as well as inside the tank cap. Your equivalent to 98 RON in the US is 93. I've been putting 100 RON (your equivalent is 95) since day one, not because I need it, but because I was suggested to do so by my dealer. In terms of power, the difference between 100 and 95 RON (US equivalent 91) is around 20-25bhp on a stock car. The only advice I can give you is go for your 93 even if you're stock. I'm not an expert I just feel safer doing what I'm told by those who are. Unless your car takes regular too so that's another story.