Read again, it is about stiffer is not automatically faster.
By what physics a beach cat should be faster, if it has stiffer beams?

And by the way, did you know that Gougeon 60ft Proa Slingshot weighted 1800lbs, build in wood 1977 or 1978. Compare this with a 40ft Marstrom x40.
For smaller boats wood is an excellent material, and if used correctly can be lighter than CFRP in some areas.

Cheers,

Klaus