Well, all of the above is the correct answer, I think. I am a long-time D76 1:1 user who has switched to PMK for the past year.(posted 8924 days ago)PMK does what it is advertised to do: appears very sharp due to edge effects and holds fabulous detail in highlights. There is some change in the rendering of mid-tones, I find. The combination of effects seems to produce that have what another writer called a "scorched look". It's a good description. I find it a bit disconcerting to look at.
D76 gives me very pleasing dark and mid-tones but the highlights often require burning in. I find it takes me more work to get to the final, favorite print with a D76 neg, BUT...
(you knew this was coming) I find that almost all of my favorite prints came from D76 negs. This is a personal preference, obviously. I prefer the greater tonal separation in the midrange and still haven't gotten used to the appearance of the PMK prints.
I plan to continue using PMK for a while longer, 'though. My tastes may change. B&W images are more abstract than color, which is what I like about them. The PMK look is (to me) more alien than D76. (You may be thinking, "What is this guy smoking?" Nothing, but I've been thinking about these differences quite a bit during the past year.)
I can't comment on grain size with much authority. My subjective impression is that the PMK dye masks grain. I shoot 6x7 cm and generally make 8x10's or, rarely, 11x14's, so grain isn't very apparent, unless you're much closer than normal viewing distance, with either D76 or PMK negs.