By accident, my wife gave us a full tank of 87 octane about 3 weeks ago on a roundtrip road-trip from Palm Beach to Montreal. The result was a heated discussion of the "right thing to do" and a few MPG less. NOTHING else. No pinging, no knocking, no anything...

The fuel economy on this 4000 mile roadtrip with premium was 24mpg @ 86mph average. The fuel economy with the one tank of regular was 20mpg... We calculated that the cost for premium is worth it as it gave a better "cost-per-mile" rate.

So, I plan to stick with 93 octane at (an average of) 20 cents per gallon more than 87 octane.