I'm a big fan of Diafine. I found it worked best with Tri-X at 800 3+3, and Acros at 100 (box speed) 5+5. Know that I reduced agitation to only two gentile inversions per minute. I got negatives that have a good density for wet printing. The reduced agitation I'm sure killed some film speed, but the rewards was a nice midrange and very fine grain. Also know that with the Tri-X I boosted the contrast with a 2X yellow filter so there was plenty of contrast to get "compensated" to avoid flat negatives.
I found that Diafine got better with use after about 24-30 rolls as it got seasoned (cross contamination of Part "A" into Part "B") where the midtones got more pronounced.
I use to shoot 100 rolls a month, one summer I peaked at 150 rolls a month for a summer, and I used Diafine as my developer for economic reasons.
Been shooting less film (Monochrom) so now I'm back to solvent developers like Microphen and Rodinal with slow speed films. I never left the game. Welcome back.
Cal