Makes me think of a story of an SR-71 mission out of RAF Mildenhall (UK). On the return, the aircraft suffered an engine unstart, so slowed to M1.8, descended to FL500, and the pilot decided to take a shortcut over France.
The French objected and sent a couple of Mirages to escort the intruder to one of their bases. The Mirages made intercept just as the pilot cleared the unstart. At which point the RSO signalled that he believed the Mirages to be stuck in first gear as the pilot hit full reheat.
I adore these kinds of Jets, they fly gracefully over a base they spy on and the second a S.A.M or some sort of Flak gun is launched or fired, they punch to Mach 3 and disappear into the gathering clouds or into the blue of the morning sky.
I ma not sure about its accuracy but this is what some sites say "Concorde would cruise at mach 2 at about 18,000 m (60,000 ft), and the SR-71 would cruise at mach 3 at 26,000 m (85,000 ft), all still in the stratosphere."