I think the SR71 has an escape capsule, not a simple ejection seat. In any case, when bailing, oxygen goes with you and when at extreme altitudes, parachute opening is delayed until something like 20kft. This gets the escapee into a warmer, breathable atmosphere rapidly as well as slowing him down for a more controlled parachute deployment.

As a guess, I would say terminal velocity at 80kft could be as high as 300mph. USAF Capt. Kittinger who made research jumps from a balloon at 102kft reached a velocity exceeding 600mph. A small drogue parachute was needed for stability until his main chute deployed.