Brick-in-the-wind aerodynamics preclude a top speed much over 60 mph. More power will overcome that, but the high center of gravity combined with the high center of pressure and extremely short wheelbase will make it a very difficult vehicle to drive at much more than 65 mph.
Personally, my Sammy is an absolute joy to drive on western Pennnsylvania backroads, which by their very existance have a natural speed limit of 45-50 mph.
Love it for what it is. If you want a fast car, buy a fast car. A Samurai is NOT a fast car.