I read that due to atmospheric conditions above 4000 ft. octane above 87 is a waste as the conditions don't support the combustion to have any benefit. I read this a year ago in Petersen's offoad mag. At sea level the benefits are tangible apparently. I do as I read and here at sea level I rock as high octane as I can. An earlier thread suggested when the timing does have to be advanced by the ecu the car can get better fuel econ, which I was also told by a friend who worked in CART-