@Horton what are you running in your Prostar? I have a 2020 with a 6.0 87 E10 seems to work very well. Adam Cord ran 39 behind it, so I guess it is ok. My Previous boat had a GT40 and I initially ran 92 octane straight gas, no ethanol, when I switched to 87 E10 there was a noticeable difference with that motor.