Roger, I'm not a member on LFPF but are people explaining why they want such a slow film? Is it based on a desire to do long exposures without ND filters etc., or is there something else? I know people used to like APX 25 but not sure if they are looking for a reboot of that or something different.
Regarding Pan-X specifically, the thing most unique about it (at the time) was that it was a high resolution, very fine grained film (therefore the low speed) that had a long scale and moderate (read "normal") contrast, as opposed to the more typical short scale, high contrast gradation of slow speed, high res, fine grained films. Of course now there are 100 speed films that do the same thing, but at the time, or at least early on, Pan-X was fairly unique in that respect as far as I know.