Well here's the thing, I know a cat will outpoint the board, and the cat might go upwind as well as a Moth, pointing higer, not going lower faster. With the spinnaker, the cat should go downwind a whole lot faster than the Moth, so, even though the kite might win, I think a good fast spinnaker cat would give a kite a much closer race, upwind and down.

There is one big advantage for the kite, besides the obvious weight vs. sail area, the kite can up up much higher into the air column, to get into more wind, vs. the Moth and 49'r sailplan, which has to stay lower.