I would buy a five gallon bucket each of C10 and C12 and see which one makes the most torque and HP Are you planning on optimizing the jetting? I've been told by some very serious and successful drag racers to use the lowest possible octane that the motor will run on without detonation or pre ignition More heat (BTU) per gallon in the lower octane according to them Keep in mind that the spark plug heat range, total ignition timing, compression ratio and jetting all need to be at there very best, optimized, to up to get the best results Good luck, let us know your results.