Check out Graph 15 here:
http://thermal-management-testing.com/ThermoChill.htm
These are the older HE series. I'd assume the graph for a PA series would start with a lower C/W for the low end of CFM, but not reach the lows of the HE series with mega-CFM.
With the HE series, you can see the graph is really steep until about 1.25 M^3/min, which acording to Graph 14 is around the power of either dual Papst 4312L's @ 12v or dual Delta 1212VHE's at 7v.
So WarlordBB's question is reasonable: where is the bend expected to be for a PA series radiator?
Note that in Graph 15, the steepness of the curve is still reasonable even at 4.5 m^3/min. This is approx equiv to Dual delta 1212VHE's at 12v. Shame there aren't more points to the right as thermodynamic laws require the graph to level out and it would be nice to see if there is another kink further on.
Shame similar graphs are not in the new radiator review at Swiftech.