If I had run my former car on 95 ron it wouldn't have been long before a piston melted, or the big ends went. I fitted a knocklink to the car and tested using 95, and optimax as it was at the time. Needless to say there was a hell of a lot of activity on the knocklink when the 95 was in the tank. I also recall a test EVO magazine done comparing V-Power, BP ultimate and normal unleaded, and a GTI was one of the test cars. I think the BP ultimate showed the highest increase in hp. Got the mag somewhere, might dig it out for a look.