Jake,
It would seem that some hit should be applied for the self-tacking jib. Even though it is smaller it is much easier to tack, especially downwind under spin.
I feel I slow the F18 fleet down, so asked to be placed in open class at Catfest. I don't know what number they used, it doesn't matter. I felt like I left alot of the decision in their hands, which isn't fair to them. The 67.9 with me at the helm is probably a good number. I looked at the TheMightyHobie18 Formula number because it, like the SX, gets a spin with no penalty and the Formula doesn't spec manufacturer of the spin. Maybe, with the jib a 67.6 (.995 hit for jib)?