I left this section for last because it should be your last resort for performance (with the exception of the Nichols flywheel). Please don't take the concept of pulling off the heads and throwing in pistons as a minor thing. It is invasive and may cause oil leaks. You are allowing your mechaincs to perform drastic changes to a perfectly fine bike. You're distrubing the belts, gasket mating surfaces, and cylinder studs. Plus, it takes the shop twice as long to do pistons than to install FCRs.
Update The PI unit that Zina had been very happy with on her mostly stock CR failed at a track day! This happened after mine started leaking brake fluid on the 916. I had time to purchase a Yoyodyne unit but they ran out of those when Z's failed!