torque isn't just a force, it's force x lever arm (perpendicular distance from axis of rotation to line of action of force) and is measured in ft x lb (or NM; 1 Newton x Meter = 1 Joule, a unit of work). That's why you may hear a stroker makes torque, because you are increasing the lever arm of the engine. Horsepower as we know it is torque as a function of RPM, its just a number; 1 horsepower is 746 ft x lb per s. Having said that, top speed would technically depend on both, but horsepower would theoretically determine the top speed, as the engine would need to achieve a certain RPM to make the wheels achieve a certain RPM.