I have been using Pyrocat-HD since one year and PMK for 2 years before that.
I have tested HP5+ with FX37 1:3 21 C 6 minutes constant agitation with Jobo Expert drum recently and indeed my EI is 500 instead of 160 with Pyrocat-HD. I measure FX37 negatives with a Heiland TRD2 densitometer. Pyrocat negatives tests have been done with standard printing time method. I hope this helps.