Is your mast a single or double diamond wire set up?
I am sure others will chime, but if a single wire, I believe that upgrading to a square top was causing some mast failures...
I thought all N.A. versions had double diamonds?
True but not all Nacra 6.0s had double diamonds and a front foil.
I believe Randy super-sized the Nacra re-designed rig called the NA for the US market and called his rig design the Nacra Express version. All of this development predated the spinnaker evolution and the various snuffer solutions. If you are updating the sailplan.... following the lead of the F18's makes the most sense... (Flat chute... self tacking jib. high aspect square top main). If you are staying with the sloop only version... then the huge jib is a big factor in going down wind.