Harry/HN:
Thanks to you both, some of it's coming back to me. I am thinking that I am wrong to posit that the stall wasn't at "high mach," given the numbers HN kindly reviewed. The conversion of CAS to IAS at high altitude reminds me of how fast the plane was traveling at stall entry ~ M0.6. I can see where one can say that it was a stall at a relatively high Mach number ... depends on frame of reference for what "high" or "low" means.
(HN, I am aware that stall involves boundary layer effects, what had me curious was the Harry's pointing out the mach elements within drag ... I suspect that was once taught to me but it wasn't in long term memory).