For those that own a Joyner 250 they have no complaints about the speed or power of this machine. Sure....they are built tough and because of that they tend to be heavier than some others that are on the market. But I would not say they are "Slow" by any means. I have some customers that have achieved upwards of 50 mph while the average seems to be about 42 ish.
If the acceleration is not good enough for you there are mods that will help get the most out of the engine and CVT. This creates a whole new feel to the machine.