Since I had some SAV loaded (GF 201) and the black test squares file was still in the RIP I thought I would test this again. 12pass Ink Density 120. Used the three values posted on this thread plus 100% K only set as output values the other values remain as various builds on rich black input values that were color managed.
The 100% K only output value still looked good, except c60m40y40k100 and c78k64y73k95 which was CMed from 0-0-0 RGB, might just looked slightly better, but It is all most impossible to tell a difference. I suspect with lower ink densities it would be harder to get a good black with a rich black mix.
I can't recall if I did a test on fabric (I suspect I did) where the Ink Density was set for 260 so maybe a rich black output value would benefit in that situation.