As a matter of fact Sandy, I am working on the article as we "speak". I am comparing head to head, Pyrocat HD, PMK and WD2D (old formula) with FP4 for silver printing on Grade 2 paper.
I will not add anything to Sandy's excellent explanation. I will only add, that using strict impartial experimental controls, so far Pyrocat HD is demonstrating to be the best and most versatile developer of the three. Better and finer grain structure, better tonal rendition and and less b+f when developed to the same CI. Of course, the proof is always in the print and there will be some of those also.