Thank you, DHO, for the suggestion. I actually have the book, and pulled it out. It has a bunch of polar diagrams for some keelboats and a few dinghies (not cats), and overall, the book is incredibly instructive.

But, Bethwaite does kind of dismiss multihulls early on in the book. His summary of their "disadvantages" - total wetted surface area is too high, hulls cannot plane, can't heel in light air for proper sail shape, high speed downwind buries the bows, they tack too slow to be tactical race boats - so their racing crews will be frustrated.

I think he wrote his book before the advent of asymmetrical spinnakers on cats with wave-piercing hull shapes.