I agree with the people who say it isn't the film.

I liked Plux-X, but one of the things I liked about it was how well it worked in Diafine. I could shoot it at box speed in D76 (or whatever) or, if needed, at 400 and develop in Diafine, and carry one film. None of the other medium speed films I've tried have responded as well, and that includes FP4+ which does get an effective boost, just not as much. People who have tried Shanghai GP3 in Diafine say it is definitely not Plus-X, in this way at least.

But that's fairly minor. I have good 400 films I can use at box speed any time I want. I switched to FP4+ for medium speed (have a few rolls of Acros to try though) and like it a lot. The differences between the two, while probably not non-existent, are simply going to be drowned out in the noise compared to the differences in photographers.