Alan, see the summaries of the Altman/Henn study and Richard Henry's tests I posted. Pan-X seems to possibly have been "optimized" for D-25 when it comes to acutance (traditional), granularity and speed.
To me it is an important film in the study of photographic science and processing. Credible, objective test results with the film helped illustrate to me how wrong we might be when generalizing regarding the working properties of film developers. The conventional "wisdom" is sometimes wrong. Depending on the film, a low pH, high sulfite developer such as D-25 can produce good acutance, while a supposedly "sharp" developer such as Beutler or Rodinal might simply increase granularity without a significant increase in actual edge sharpness (ie traditional acutance). Studies such as Altman/Henn which involved Pan-X helped me realize how critical the film type is when it comes to developer characteristics.