With respect Mark
Pyro is considered by many to have had its day, but in respect of modern sensitive materials it is suggested that its wonderful versatility is awaiting rediscovery. Let us hope that the younger generation will not be content with anything that falls short of that standard of perfection “pyro quality.” (quote from 1941)
Steve, I see the "Resolving Power" as the result of the combination of the film, developer and technique. In this respect I'd put Xtol and Rodinal on a par with Pyrocat out of the developers I've used, yes there are developers and techniques which might give more apparent sharpness usually with increased grain which reduces "definition" of fine detail, or compromises the tonal range.
Originally Posted by Steve Sherman
There's unique characteristics of Pyro developers that are harder to define but it's the good acutance and micro contrast along with the ability to hold a good shadow detail and delicate highlights. As you say “it is the combination of several small gains or traits when joined together yield a significant result in the Process.” I've said many times that Pyrocat HD is like Rodinal on Steroids it's a remarkably good developer.
This is what's known as “pyro quality.”
This quality is by no means imaginary, and may be attributed partly to the faint warmth of even a non-staining pyro image, and largely to the fact that pyro reduces with perfect proportionality,that is to say, it produces a characteristic curve which is straighter, and less liable to distortion than any other reducer,in spite of varying conditions of use. (quote from 1941)