Monohull people are always looking for reasons to bar multihulls. At Key West Week they allowed multihulls for the first time. During the regatta a port tack monohull hit and sunk a catamaran on starboard. The administration immediately blamed it on the catamaran because they sail strange courses. Hmmm! But the cat was sailing upwind, zigging and zagging just like a monohull. They went on to ban multihulls from the regatta, even without a reason to do so.
As for mast floats, we had a MacGregor 36 cat that had a big float on top. It was very aerodynamic and certainly did not hamper speed. We were faster than Macs without the float. Also, the boat had a waterbag system. While on its side you used the spinnaker pole to put the bag out away from the bottom of the boat and the jib sheet around a winch to right it. We never went over, but the previous owner said it really worked.