Gerry, that's standard mx pace on any mx bike.  It's a rather hyper activity.   However, only the pro's do the big air.  Us normal guys like our bones intact.  I remember the thrill I used to get, about 17 or 18 years old, wind the bike up as fast as I could across a farmer's field, catch a rise and flyyyyy.  Low altitude.  One day there was a strong cross wind and I drifted several feet sideways before reconnecting with terra firma.  I'd say 50 or 55 mph.  Let's just say , don't hit a rock!!