I was wondering what rating you get sailing two-up on the FX-1? If you look at the USSA-Portsmouth Yardstick Multihull corrections, you only get a multiplier of 1.01 for sailing in excess of 130% of the class minimum. There does not seem to be a correction for two-up on a single-hander. I often race with two on my FX-1 with the jib. Seems about as fast as single, but the corrections work against me because you take a .975 hit for the jib and only get 1.01 for the extra body, so that you end up with: FX-1 solo, no spin = 71.2 FX-1, 2-up w/jib = 70.1 This says the 2-up w/jib is faster by about a minute per hour sailed
I prefer sailing it 2-up (I actually agree with Wouter that it may be too buoyant, especially for my mere 160 lbs), but I don't think it is that much faster.