My 32 can do 70 also but I have to go under the boat and spin the little speed wheel by hand.
I think the speed record for a Marinette has been broken by a 1976, 37' sedan. 48mph with twin Crusader 496ci engines. He is docked across from me. Boat sounds awesome and the torque is amazing.
Yes, the steering does gets squirrelly at those speeds since there is virtually no hull in the water.
-Karl
1986, 32' Sedan, twin 360ci, 275hp Chrysler's w/ K&N flame arrestors