Yes. I run creduce on a 2x10x8 ppc64le machine often and I definitely don't want to use 160 tests in parallel...
Aw come on, that would be awesome. You should try it once just to see what happens.
But anyway I just pushed some code implementing the change I mentioned earlier today that (1) tries to detect physical instead of hyperthreaded cores and (2) backs off from the full N, maxing out at 4. I think these are good defaults and Eric can pull out all the stops on the big iron using "-n".
John