You should definitely run 91+ octane. The 850's can run 89. All nortons have excellent original valve seats. The ignition curve is the hardest thing to satisfy even with 91 octane. I run a RITA for my combat and have never looked back.....it has better curve for the combat. They are no longer made but old ones are always showing up. I fix them, so even bad ones... can soon get you going. I've not tested the newer stuff being offered.