They've been clocked at 80+. Remember though, they're not going to be descending at 80mph, which is really the only time you'd need to worry about collisions.
That is definitely not the only time you need to worry about collisions, it is the most dangerous time but not the only time, as there are many things taller than 200 ft, as well as birds and unequipped vehicles using the airspace in an unauthorized manner for you to worry about.