Jim,(posted 8698 days ago)I've developed all four films mentioned, as well as others, in PMK. Of the four films I like FP4+ the best, Plus-x next, then Tri-x and the Delta films the least. BTW, of all the films I've tried with PMK the Kodak T-max films are the least satisfactory.
I would urge you to try exposing the FP4+ negatives at a lower EI. As with Plus-x, I rate FP4+ at either 64 or 80, depending on the meter/camera being used, and also develop it (120 roll film and 35mm) for 10:00 at 68 degrees. The additional exposure really supports the low value densities.
Good luck, Sergio.