Owner's manual page 164.
Fuel Quality
Choosing the Right Fuel
use only unleaded gasoline or unleaded gasoline blended with a maximum of 15% ethanol in your gasoline vehicle.
I stay away from blends.
Octane Recommendations
We recommend regular unleaded gasoline with a pump (R+M)/2 octane rating of 87. Some stations offer fuels posted as regular with an octane rating below 87, particularly in high altitude areas. We do not recommend fuels with an octane rating below 87.
To provide improved performance we recommend premium fuel for severe duty usage such as trailer tow.
Do not be concerned if your engine sometimes knocks lightly. However, if it knocks heavily while you are using fuel with the recommended octane rating, see your authorized dealership to prevent any engine damage.
For myself at right around 70 cents a mile to drive. Another .0125 cents per mile for 93 (at 30 cents per gallon), is a non issue, if it did offer an extra 15hp/tq. Have only used the 87 octane (4,100 miles) so far and never noticed any knock. I'd really like to know what real difference using 93 would offer; but short of a drag strip stop clock and test track mileage, back to back, who's to know. There are way too many variables to real world mileage to know for sure. As the first real road trip nears, I'd like to split and run the 93 for the return, although I recall not all states have it. Anyway the return trip is not the same weather or head winds; so forget the mileage test and that seat of the pants is not going to yield much fact without the clock.
I'm sure Curiosity will most likely get the better of me. :devil