I've only shot one roll of Classic 400 in Diafine, with the sole purpose of finding an E.I. for it. Judging by my non-scientific results, I'd rate it at 200. Anything above 400 was just too thin for normal grade printing, and rating it at 200 gave better shadow detail without any losses of highlights (a white t-shirt in full sun had detail in the contact sheet).
I've never shot Foma 400, but both Foma 100 and 200 look very good at their box speeds (better than their Classic counterparts). So, as a complete guess, I'd rate it at 400.
André