Just a question for all you HCH and Prius owners: have you noticed a significant difference in fuel economy between octane grades of fuel?

The reason I ask is because my gas-hog Ford Ranger pickup gets ~10% better mileage on high octane verses low octane fuel.

And the price difference between the fuel grades is <10% now, so it seems to me its more cost effective to run high-octane and pay the slight increase in cost, in order to get substantially better mileage.

Any thoughts?