Google search for Virus boats, they are a French company which makes a 21 foot trimaran. You could buy just the center hull and add your own bigger ama's (Nacra hulls). The only advantage to the Tri (in that size range) is the larger center hull allows you to cary more people and remain drier than out on the hulls/tramp of a cat. It will not be faster due to the weight. On the cg thing, if they built cats as wide as they are long, like a 60'tri (60 feet wide) the righting moment would be the same, right?

But for more speed, you want less drag (wetted surface), ie. sail it (cat or tri) on one hull as much as possible, so in lighter air, you don't want more righting moment, you want the cat to fly a hull as soon as possible. Wider means heavier too, if just in the extra weight of the longer beams.

I once asked Ian Farrier, designer of the Corsair Tri's why the ama's were so small. I figured bigger, fatter ama's would allow the boat to fly the center hull like the French Open 60's do all the time. He said there are two reasons: the smaller amas will go under water at a lower wind stength which -should- wake the crew to the fact that they should be reducing sail area. Also if the ama's were much bigger, they would have trouble getting them to fit on the trailer when folded. Still, I would love to see a F24 with the F28 ama's on it! I wonder if they could do that as a go-fast option?