I used only premium stuff until I compared the performance to lower grades. Personally I have not seen any appreciable difference in power. With prices going up I only buy middle grade or lower now. Heck, years ago when I could get 104 octane I tried it in my V8 Ford with stock compression, but still felt no difference in power. Before ECUs (yeah I remember that), I think detonation was more of a problem. I've never had an ECU equipped car so much as ping once.