I used Diafine at one point, was not impressed. However, with TX or HP5 it produced between a half and a full stop speed increase (probably from the phenidone) without excessive grain if you use the Diafine A and the DD-76 B. Save the Diafine B for cleaning your oven.
It is a terrific cleaner. Mine leaked out of the jug once onto a tile floor while we were on holiday---it had mostly crystallised by the time we came home. I have never seen grout so clean in my life!
I actually quite like the look of Tri-X in Diafine, though I agree that EI 1600 is *very*, um, optimistic. I also get a fair amount of use out of the stuff for long (tens of minutes) nighttime exposures, but that's mainly for the compensation and I suspect many other divided developers would work just as well.
-NT

