The terminal velocity in the stratosphere is significantly higher than at sea level, and the speed of sound is lower, at around 670 mph. Joeseph Kittingers' record was 614 mph, which is not that far off the sound barrier.
Excellent article. Note though that the pilot did not technically eject, his ejection seat was ripped out of the disintegrating plane intact by aerodynamic forces. Though the experience is probably applicable to the case where a pilot were to intentionally eject at Mach 3.
Pilots have ejected out at Mach 3 from a SR-71 http://www.alexisparkinn.com/sr-71_break-up.htm
In that accident, the pilot ejected without major injury, but the co-pilot was killed.