9853 will give you more power, I would try that first that i would go with reducing the head clearance by .1 at a time.

I personally only reduce head clearance as the engine gets older and i start to have random flameouts. I mess with the clutch and pipe to get the power i need. My go to pipe for good al around performance is the 9901. The 2096 does not give me the feel i want no matter what i do. The 9853 will give you the best power for a nova branded pipe..