The pyrocat stain is a factor when printing on VC paper as well: It has about the same effect as full yellow filtration - i.e. very low contrast. Expect to be surprised by the necessary change in filtration!
I have tested both a Pyrocat HD negative and an ABC pyro negative using a Xrite 310 densitometer. I read the effects of the stain on the different color channels. These are my findings:
Visual density 1.82 Blue Channel 2.17
Green Channel 1.87
Visual density 1.91 Blue Channel 2.41
Green Channel 1.95
Actual tests of the effects of stain of these developers show a minimal effect in respect to imparting green (low contrast). As one can see the effects at a fairly high density in both cases was .05 in the case of Pyrocat and .04 in the case of ABC pyro. This is not surprising since Pyrocat's stain is brown in color wheras ABC pyro is more black.
I have not used PMK since I have long considered the greenish general stain imparted by that developer to be counter productive to the benefits of proportional staining of the high silver densities in the negative. Furthermore PMK would by the nature of it's stain color be more prone to passing green (low contrast) light into it's emissive path. PMK is a good developer and many use it to good effect. I, however, do not favor it for my work.
The tests do indicate that the blue channel readings show that Pyrocat has a lower tendency to limit the passage of blue light through the emulsion then ABC pyro. (.35 in the case of Pyrocat vs. .50 in the case of ABC Pyro). This increased density represented to the blue spectrum would indicate that ABC Pyro has the greater contrast reduction potential when used with VC materials. This would indicate that the characteristic that makes Pyrocat such a wonderful developer for use in Azo are limiting to a degree with VC filtration. However, the effects of the proportional staining in overall contrast is probably offsetting a certain degree to the limitations on the blue spectrum passage.
In my work enlarging Pyrocat negatives I have not found that the effects have been that of full yellow filtration. I do not have an actual comparison of the effect since I have not shot and developed the same scene shot on both a Pyrocat developed negative and a none staining developer negative. I have noted however beautifully differentiated upper tonal values (VI and above) when using Pyrocat HD.
When we get into the region of densities most often seen with enlarging the following are the results with Pyrocat.
Pyrocat HD Enlarging
Visual density 1.10 Blue Channel 1.39
Green Channel 1.13
This would be expected and shows the proportional nature of the stain effect on negative density when compared to the examples above.
I would tend to believe that if any staining developer would have the contrast reduction potential in use with VC materials then it would be PMK.