71° on CPU A with no CPU usage whatsoever? No wonder the boost fans run at 2200RPM!
Did you check your thermal paste?
I know that your CPUs have a TDP of 130W, but still, those temperatures are little too much.
My boost fans are constantly at 1200RPM and I've never seen them above 1500 with 100% CPU usage. But then my CPUs are rated with 80W TDP.
I wouldn't recommend forcing the RPM do lower speeds, as it would result in even higher CPU temperatures. Keep in mind that the Nehalems maximum core temperature is around 90° and iStat Pro doesn't read the core temperatures, rather than the HS temp. You can add more than 10° to get the approximate core temperatures.