Here in Italy we only have 94 and 99 octane, at 1.30Euro and 1.35Euro respectively, with Shell selling 100 octane at an obscene 1.45 Euro so only those with Shell coupons buy any.
My own experience with cars is that if you fill up an _
empty_ tank with 99octane you spend 4% more and get 5-8% better mileage and performance.
So for the long runs I'll use 99 octane, for city commuting I'll settle 94.
87-85 octane we call "farmer's tractor" fuel, used to be issued to the Army in the '60s but that's long gone.
Anybody tried kerosene?
Maurizio