It'll hit 100 if you shove it off a cliff. Seriously, your question cannot be answered without a lot more information. Year, make and model to start. Stock or modified? On what terrain? Your question is like asking how much is a bag of groceries.
1989 Yamaha Bravo 250 Top speed on a Bravo is 40mph on ice with a tailwind. My 1982 Yamaha Bravo has been clocked at 58 mph with a 170 pound person on it.....Mt 1973 arctic Cat El tigre 250 would do...