I am trying to find the right fuel for my 2001 40hp-merc cycle. The manual says 87 octane or any grade above. The 87 pushes my boat at about 23-mph (speedometer). While out on the water I ran low on fuel and the only gas at the marina was 92 octane. I got some and later in the day I happen noticed that I was running almost 3 mph faster at wot. I backed off the throttle because I was afraid the higher octane would run the motor hotter than desired. I used up that fuel and now I am back to 87 octane. The motor seems ok but I lost those 3 mph. Does anyone know if using 89 octane will give better performance than 87 without running hot?