[Kracka]

Assuming equal quality of gasoline, he will get better performance and mileage from 87-octane fuel since that is what his engine/ECU was designed for. The ECU will not add more timing as the gasoline octane increases; which is the only way he would get better mileage and power from his NT engine. Again, this is assuming equal quality is the grades of gasoline, which should stand true using a decent brand such as Chevron, Sunoco, BP/ Amoco, etc.