Bill Tindall, E.Tn.
A $500 solution has been proposed to solve a problem I am uncertain exists. That cost might drive someone to buy a thickness planer and have some change left, or an M2 blade. David could easily do the experiment. But like some of the later experiments details between users would render the conclusions uncertain among users whose conditions deviated from David's. My details might avoid loss of hardness and yours might not, it could be argued, and the experiment would settle nothing.

That said, has anyone suspected loss of hardness from grinding under careful conditions? I don't grind to the tip and anyone that does with a wheel is further removing the resulting tip with subsequent edge refinement. This situation would seem to dismiss this heat concern. I, and maybe others, don't try to get a uniform hollow. If heating is an issue the thicker places would heat less, be harder, and wear less, which should be apparent when examining dulling. In fact this experiment could be done by anyone concerned about their technique.

I only hollow grind when edge refinement finally removes the hollow. If I lost hardness from grinding the blade would become harder with each subsequent sharpening until I ground again. Had anyone seen this effect?

Have any differences between the high speed steels like M2 and CPM 3V and those tempered at lower temperature been revealed?

Loss of tip hardness will result in the tip folding in use. Might take a magnifying glass to see it. I saw it with an unusually soft Sargent blade, soft enough to scratch with a file( Rc?).