I think you are on the right track. However I would use the old pinhead sail and get back to the original configuration with a 66.4 number. Most of the difference in the MX version is in the jib anyway. Also wouldn't you take the L4 hit of .97?

So here is what I have for you.
66.4*1.076(UL)*.97(L4)*.96(SP)=66.53

66.53 would be a little easier to sail to than 64.39

Mike Hill
H20 #907