While I don't think it really makes a difference, there is a simple and very effective method for more octane if you want it. For each 15 gallons of gasoline, add one gallon of virgin lacquer thinner. I do this in my GT350 because 93 is not enough with the compression the 289 has. It goes to 98.3 octane (had it tested). I picked this up from the turbo crowd of the Buick Grand National Club years ago and have used it in the GT and the Cobra just as long without problems. To calm fears, read the back of a can of Super 104 Octane Booster...almost complete toulene...which is lacquer thinner (read the can). I have been told that the Super 104 has a touch of Marvel Mystery
Oil in it as a lubricant/cleaner, but I just run the thinner.