This was my research during an internship at Renaissance Press a few summers ago. My goal was to quicken the development of calotype negatives to a few minutes instead of the 30-120 minutes necessary to build up enough density with gallic acid. (Pyrogallol is too aggressive and produces too coarse of grains for my taste.) Thus I began experimenting with Metol developers.
I would consider this research incomplete, and will begin more tests soon.