The way the listing is written, it states estimated speed 200mph. Then, as an option for greater speed, 2 nitrous systems can be added. If it is pulling max rpm without nitrous, the gearing would need to be changed in order to take advantage of the extra power (whatever that is).
Nitrous is usually used to increase acceleration, not top speed. If the gearing is designed for a large nitrous injection the acceleration without it will be very poor, especially in a vehicle weighing 2.3 tons!