Jdef,
I can address several of your questions based upon my personal experience with both developers. I have used ABC before I switched to Pyrocat. The matter of staining and VC paper is not so much a matter of stain as it is the color of the stain.

In pyrocat the brown stain color does not have the effect of reducing high print value contrast to the extent that ABC does (due to the brown versus greenish stain). Green is the light color that gives a reduction in contrast with VC papers whereas blue serves to increase contrast. I noticed a marked difference with the first Pyrocat developed negatives that I enlarged on VC paper. Additionally I have found that Pyrocat does not suffer from the uneven development that I experience with some of my ABC negatives.

I have found that in several films that there is an increase in effective film speed. Bergger BPF 200 for instance benefits by 1/3 stop over ABC.

I would concur with Clay that Pyrocat is a good developer for a variety of applications. The only area where ABC may have a slight advantage to Pyrocat is possibly in shadow tonal separation. I believe that Sandy King addressed that on the Azo Forum sometime ago. Pyrocat does offer better highlight tonal separation then ABC however.