1991 22RE: 85 octane (23 mpg/ 5 tanks in a row)
I did a similar test to Big Mike's. I ran several tanks of 85, 87, 89, 91, and 92. I got my best mileage at 85 octane.
I'm pretty sure this happens because of the altitude here.
At sea level, (14.7psi) and the yota compression (9.2?) the internal cylindar pressure comes out to ~135 psi. Here at 7200 feet the atmospheric pressure is more like 11psi, so the cylindar pressure is reduced to 101 psi. At that pressure, there's absolutely no need to run a ping-resistant fuel. 85 octane costs less and lasts longer (better mpg) than any other gas I can buy.
My advice would be to try everything out for yourself. See what works best.
