Marginal to none. More effect can be had by adjusting driving style and tire pressures. Bang-for-buck the net effect is it will cost you money to run high octane fuel over and above any savings you may make in fuel consumption.

2002 Sporty , Ironman 2.5" spring, 2" body, 15 x 7 ROH wheels, K&N, 15 x 10.5 Simex Centipedes, Powerchip 91.

"Never argue with an idiot. They will bring you down to their level then beat you with experience!"