A common factor that you will find that every Worldclass race engine builder has is that they build every customer's race engine as if it was their own. Some of my M8's have accused me as being a twit, due to the fact that I sometimes I talk to a race engine's parts while I am building a engine for my customers or myself. I tell my M8's that it is a way of showing respect to the parts and their mission to produce horsepower and win races. That being said it bothers me when I see my customers not feed their engine correctly.
Some Racers make the mistake and believe that an octane rating is the most important factor in selecting a Race Fuel. Their misconception is that they believe that the higher the octane number of a Race Fuel, will mean that the fuel will produce more power. This thinking completely ignores the critical factor of a Race Fuel, the flame speed at a given cylinder pressure. Gasoline's octane number only measures a fuel's resistance to detonation and pre-ignition. It has no relationship to flame speed, which is critical to maximizing cylinder pressure and creating horsepower.
Race Fuels are designed to maximize the flame speed at high cylinder pressures of a race engine. These fuels are also designed for engine speeds above 5000 RPM, Aviation gasoline is designed for relatively low compression engines operating in the 2700-2800 RPM range at 8000 to 10,000 ft. altitude. When compared to Race Fuel, the transient response which is the measure of an engine's throttle response and the ability for a engine to rev quickly of Aviation gasoline is poor, this is due to the result of the blend of the fuel and is no way measured by the octane rating.
Aviation gasoline has a lighter specific gravity than Race Fuel instead of weighing about 6.1 to 6.3 pounds per gallon like Race Fuel, it weighs 5.8 to 5.9 pounds per gallon, . This characteristic requires much richer jetting with Aviation gasoline or a lean condition and a burned hole in a piston will result. Another major difference in Aviation gasoline is octane quality. Aviation gasoline is low on octane, and has a lower volatility and does not evaporate as quickly, this is a requirement for high-altitude use. Race Fuels are more volatile fuel than Aviation gasoline, the reason for this is the base fuel and the additives that are put into it. The volatility of a Race Fuel is due to blending of butane, the desired volatility depends on the ambient temperature the hotter the weather, the lower the volatility.
In conclusion the choice is left up to you, a word of advice though, a 2 degree advance of the ignition requires a 1 point increase in a fuel's octane rating.