Greetings,(posted 8543 days ago)The finest grain and longest tonal scale will not necessarily give you better negatives; it depends on your application. A POTA developer will generally increase the "tonal scale" (decrease the contrast or Gamma) of any film. One of the finest grain films is Kodak's Tecnical Pan. Developed properly in a POTA developer, it can yield a 10+ stop range, BUT it's extremely slow (ISO of 25 or less) and a difficult film to tame. You would probably have to run numerous test before getting the processing time/agitation correct.
The Darkroom Cookbook by Anchell & Troop is an excellent place to start searching.
Regards, Pete