You are of course familiar with that most popular single handed racing dinghy, the Laser. It has a two peice aluminium tube mast and they do offer two different size tops, for a smaller mainsail. It is completely unstayed and rarely break. I would think you could come up with some sort of very thick carbon sleeve mast section, that along with stays, would work on a cat, and not be too fragile. The biggest advantage might be the ability to run a shorter top section for those really windy days, but then you would need a second main or a reefing main sail.