Old Pilot says that the 800MPH speed was the fastest. A number of pilots/RSOs ejected from SR-71s. Some lived, some died.
I'm sure there were others that ejected from high-speed aircraft (I imagine a number punched out of F-104s and F-105s at supersonic speeds.)
Also, I believe there were rocket-sled tests done at supersonic speeds.
http://www.ejection-history.org.uk/Aircraft_by_Type/SR71.htm
The whole list:
http://www.ejection-history.org.uk/0000/AT.htm
Be that as it may - the sudden wind blast would tend to bust you up pretty good.
As far as Felix goes - his speed was vertical against almost NO ATMOSPHERE at all!
