I’ll give this a go, though honestly for the stuff I use Parallel for, I don’t think that Parallel is the bottleneck; usually I use parallel to queue up like 50 ffmpeg or imagemagick jobs, and the vast vast vast majority of the time for those (I would think) would be consumed by the main program, not Parallel.
Maybe I have a really atypical workflow on this? Or maybe I’m misunderstanding something?