I suppose that two pumps aren't relevant at this point... I must be loosing track of this thread! The first graph you posted shows Sim20R and Sim20RZ, I thought they were about the same pump, for some reason. I understood that putting pumps in series does not result in a full doubling of the pressure: am I off my rocker?
Nah, just OT, sorry.
From both graphs you've posted, I'm inclined to believe that blocks in series work best!:shrug: