Even at almost $6.50 per gallon here I wouldn't even want to consider using low octane fuel. The fuel cap says 98 octane, so I pack the best fuel I can conveniently get my hands on into the tank (e.g. Shell optimax), no questions asked. I'd rather not compromise the engine and performance. Same goes for oil. Yes, I believe in the holy manual.

While I lack the finer technical skills to reason out that approach, I can imagine what impact it would have on my own performace if I was living of Tesco value meals alone..