The quality of the racing is surely more important than the speed of the boat.

I raced on two evenings last week. One evening sailing the Stealth in a cat class that consisted of two boats. And the other evening doing downwind trim on a J/80 in a fleet of 18 yachts. Yes, I went faster on the cat (according to the GPS vmax was 14.2kts on the cat and 14.1kts on the J!) but which was the most enjoyable race? Yesterday I sailed in a tuneup regatta on the J. Light winds and some brilliant racing against a J/92S, Delphia 24 and a Corby 29 at the front of the fast class (which we won:)).

So, enough of the mono/multi slagging. Get the best of both worlds and sail both!