Wouldn't it be funny if Plus-X were actually just a reformulated/sensitized Panatomic-X such that the speed gain is there? Maybe Pan-X is just a less sensitive long scale film as opposed to something like Pan-F which is a true slow speed fine grain film. I'd think Plus-X with an ND filter or just shot at a slower speed could offer a pretty decent low speed medium contrast replacement. Certainly not worth pining over something that disappeared ages ago and we know will never come back in it's original form.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.