Depends upon gearing and installed motor.
Assuming stock equipment: HPI 21 engine, 14T clutch bell and 52T spur gear.
Several years ago I read an article that stated this combination hit 32MPH.
My Savage .25 bone stock tuned well would do 36.....clocked with police speed gun. So I would agree with about 30-32 or there about for a .21. Enough to explode if it hits something good and solid......like a brick mailbox.....I hate brick mailboxes....evil