Dave,
A few years back an E Scow sailor was speculating that if he had the right conditions, he could beat Daddio in the Mug Race. We sailed down that year and he launched from the Palatka marina and met up with us at the dog leg as we were approaching Palatka. Havinging sailed the 30+ nm we weren't interested in setting the chute on the light winded broad reach to the Holiday Inn. He saw us coming and did a 180. He set the chute and started drag racing us with his self given head start. It was comical for us(Charlie, Pam and me) to just sit on our butts and sail past them with just main and jib. Charlie and Pam never sat up and I only sat up to see where we were going and for the occasional trim of the main.
Needless to say the E Scow sailor never said a word about it again. That year it seems that we passed him the next day not far from the same place we passed him on the way down.
As Wouter alluded to, it is pure fantasy for a Melges 17 sailor to think he is faster than an A Class cat or for an E Scow sailor to think he can beat an RC-27. I would be really surprised if the fastest monohulls had performance curves that came close to most average catamarans under ideal conditions (for the monohull).