If, as you say, Mach 14 (4764.06 m/s) is the fastest we can go, then those ships were going about 19060 m/s. Now, in order to be making any real headway in the Universe, they'd have to be going the speed of light - even at that speed, it would still take about 4 years to get here from the closest star to Earth.
The speed of light is like, 300,000,000 m/s.
So really, that closest star is like, the number of seconds in a year times 300,000,000 meters away. If they were only travelling 4X as fast as we can, they'd *still* need to be going a HELL of a lot faster.
That was based upon measurements allegedly collected here, within the atmosphere. What kind of retarded aliens would gun their most powerful engines/propulsion devices before they got out into open space?