Steve made many good points and I can think of one other factor to throw into the mix of trade offs to consider. As hulls move through the water they develop a boundary layer along the hull. Because of pressure variation along the hull the boundary layer eventually becomes unstable and seperates into a broad turbulent wake. Resistance can be minimized if this boundary layer seperation is delayed until as far aft as possible. The monohull strategy for doing this is to provide a asymetric waterline plane and aft rocker so the widest dimensions are aft of the midpoint. Sort of a pear shaped distribution of area. Of course, like everything else in boat design, if taken to extremes asymetric hulls perform worse than more moderate shapes.
As applied to catamaran shapes, it's more important to arrive at a shape that can go through chop and carry sail with little fuss than trying to minimize boundary layer friction. It's just another of a long list of things to keep in mind.

Kevin Cook