As I recall the SR-71 was not an exit by an Ejection Seat but was an ejection of the Seats and Occupants following the aircraft going unstable following an engine failure and breaking up.
M3.0+ inlet unstart?
Only a couple of years until the 50th anniversary of that accident.
Mach 3.2, 100K' altitude, Russian titanium, first flew (in A-12 guise) in '62. Remarkable aeroplane.
http://www.barthworks.com/aviation/sr71breakup.htm