Just out of curiosity, when using this approach with general purpose developers, where does the film speed tend to fall in comparison with the ISO speed?
Very developer dependent, and dilution/agitation also seem to have a huge effect, with lower dilution sometimes giving compensation effects (so in essence, higher film speeds), and with more agitation generally having the opposite effect.
For example - I do all my sheet films with rotary agitation. It lets me be super economical with chemical use, and gives me perfectly even and consistent development. But the constant agitation has a trade off of lower film speeds. I have tried to compensate for that by generally using weak concentrations and longer times, but HP5+ sheets in HC-110 1:100 still only give me an effective speed of 250. Rodinal is even worse with FP4+ sheets - I have to shoot at 64 to get proper shadows, even using 1:50 or 1:100.
For roll films, I use steel tanks, and the most I ever agitate is the Ilford standard (10s at the start and 4 gentle agitations over 10 seconds every minute thereafter). With some developers like Pyrocat HD, I'm actually doing basically EMA with roll films (1 minute to start, 5 seconds of gentle agitation every 3 minutes from there). That seems to buy a lot more film speed, especially when paired with phenidone-ascorbate developers like Instant Mytol and FX-55. I get full box speed with Pyrocat HD and FP4+ done this way, and about 1/3-2/3 of a stop boost with every film I've ever run through Mytol (Delta 100, FP4+, HP5+).