[naz]

i think it is almost certainly in your head dude... the only way higher octane fuel offers more performance is if your ECU is setup be aggressive to advance timing and/or boost if no deto is seen... i'm like 99.9% sure that a stock focus ECU doesn't do that

the only advantage i can see for a stock focus using higher octane is that the fuel is cleaner and less likely to leave gunk in the fuel filter

as for whether a 91 octane flash is better.. on a stock focus i don't think it will make that much of a difference..