[sbasak]

Last week in UK BBC's Fifth Gear show, they conducted a test on how high octate fuel increases performance of the cars.

The result

For small cars (~ 100 hp) = no power increase at all
For medium cars (~150-200 hp) = less than 1% of so power increase
for sports cars (~250 hp) = appx 5% power increase

It didn't tell anything with fuel economy though - but suggested they will remain more or less same.

Verdict was:
For normal cars, high octane fuel hardly produce any advantage!