Thomas your jump from graded #2 to VC #3 seems logical to me, at least directionally.
I also agree there might be significant differences in graininess depending on the developing agent(s). Not only that but some formulas stain more than others, and more stain means less silver, and more grain masking. Plus there are some formulas like WD2D+ that stain yellow-orange. Pyrocat is reputed to be relatively fine grained although I have not tried it myself.
It's funny this thread came up now because as it happens I had just ordered a series of different formulary developers for some particular experiments and on a whim decided to throw in a few tanning developers just for fun since I have not used one in quite some time. I might try them with 35mm. Never used a staining developer on anything smaller than 4x5 before. I doubt I'll end up switching, but always fun to rediscover things. For good measure I included The Book of Pyro in my order. Finally gave in on that one.