Well I have used both and from my limited experience with PMK pyro the biggest difference I saw was better highlight retention. XTOL for the most part gave me flatter negatives than I normally like, and I found to correct that I had to change(increase) my agitation procedure compared to any other developer I have used. But it does give a slight speed increase which is welcome. I use PMK, I guess, mostly as extra insurance against blowing highlights. Of course that depends on what I shoot.