Octane requirements of engines increase with age due to deposits in the combustion chamber, so after you get 25-50K on the vehicle, you might see better performance using the 93 octane (modern engines have knock sensors and retard the spark if it senses the engine knocking. A retarded spark will diminish performance somewhat). Contrary to what some people think, it's the old. hih-mileage vehicles that need higher octane.