I run amsoil in my engine and use 110 VP leaded mixed 50-50 with 91 octane and get phenomenal performance,a little expensive but hey you wanna play you gotta pay.
Is that Amsoil 0W40?
Royal Purple recommended their 10W40
Arctic Cat recommends 0W50
I guess they are all similar
What kind of oil filter do you use?
Do you always run 91 Octane gas?
Higher octane gas won't do squat for performance in these machines, and in some cases, can even rob power. Changing the compression in the motor would come into play with higher octane, but not stock. Amsoil is about as good as an oil you can get, 0-40.