Last time I used real Diafine, I found Tri-X (in 2003, and it might have been 1990s Tri-X, I don't recall) came out at EI 640 -- that's 2/3 stop increase. Tri-X has been reformulated at least twice since then, IIRC, and the Anchell "Diafine" was never confirmed to match actual Diafine.
The things we know for certain: Diafine used phenidone and hydroquinone, which combination will usually yield a modest speed increase when developed to normal contrast. As noted above, film has changed a
lot since Diafine was introduced, and modern film carries less developing agent into the accelerator bath, so you may be getting less development, giving lower contrast, and offsetting the expected speed increase.
If it's two-bath convenience you're after (little temperature control needed, timing very much non-critical, doesn't even need agitation other than on filling, to be sure you get the air out), shoot a bracketed test roll to find your correct EI and enjoy the easy way of development. if you're after a speed increase, I'd suggest selecting any phenidone- or dimezone-based conventional developer (Ilford PQ Universal, Xtol, E-76, etc.), diluting as far as manufacturer's data will support, and developing as if for a 2 stop push, but agitating only 10 seconds every third minute after the continuous first minute. This will get all the true speed you'll ever see with normal contrast (you may need to adjust your time a little, depending what you consider normal contrast).
And if you're just experimenting to see what you like, carry on.