Boats dont scale like that Pete. Aero and hydrodynamics scale differently, and the loads scale like crazy with increased size. E.g. banana foils and foiling C cats are not fast compared to the top boats, but a foiling moth are really fast compared to a scow moth.
If you go back to the '88 challenge, the USA team buildt what might be considered a scaled up C cat for the cup. But what they really did was get the best C-cat brains and put them in a room with some really good engineers and builders (Morelli, Rutan etc). They picked the best aspects from the boats they knew and adapted this to the new platform.