Using a octane rating above the nominal 93 gets you nothing. It's not the lower 91 that yields lower MPG; it's the ethanol blend. 91 lowers performance (peak power/torque) but has little effect on MPG because the ECU adapts to the lower octane with the appropriate engine mapping.we have selected gas stations that carry 100.
and yes it is very pricey. There's one in Newport.
Ideally these engines should get ethanol-free 93 octane gas - to get the advertised performance/MPG.
One can blend 100 octane with 91 to get the prescribed 93 (no benefit in going above that). Doing that one gets the nominal performance. But that does not improve MPG, because ethanol is still there and in addition 100 octane usually has ethanol.