During my Air France Concorde flight, I photographed the bulkhead Mach meter. This was about the fastest that we went; Mach 0.95, which is the equivalent of 723 miles per hour. Note that from JFK to Detroit it's pretty much all over land so you can't go supersonic like you can over the ocean. Still, 723 miles per hour is extremely fast, given the fact that most normal jets cruise at 550 miles per hour