Descending from FL370 the other day I decided to see what she would do. At High alt passing through FL330 she started buffeting or shock stalling right around mach .79 at about 300 indicated, I don't remember the true airspeed...if you have one of those fancy cx-2 flight computers and know ISA temperature for FL330 i suppose you could figure it out...off the top of my head i think its...around -50C. Remember if you begin to buffet, throttles to idle and use nose up trim to recover from tuck under/buffet so as to not overload your airframe with too many g's upon recovery. I've noticed that right around 360mph down low you tend to lose your elevators first and then your ailerons next without any high speed buffeting. Approximately 15 - 18 k and below....