The energy numbers should be a valid way of measuring it, but you’ll need a long time to get a good observation. The numbers accumulate fast hits in to one number, and the time period most likely won’t be exactly equal to your tool speed, so there’s going to be some variation between some action speeds depending when you stop counting.
In my post I basically did it by tuning a metronome to the hit sounds, it’s here for those interested
The result was that mega fast adds to the tooltip number (which includes skill and forge effects)