If I were to guess, I think maybe I can shave 0.25 seconds off my lap times by using 100 octane. Not really much of an advantage, but every little bit helps. The stock Crossfire runs perfectly on the 91 octane that is recommended by the manufacturer so unless you're really going to compete in the car, I wouldn't waste the money.

PS: Have you had the opportunity to run at Bramshatch with the Crossfire?