[Mark Yacavone]

Jim,
Both the diode and the roller sprag perform the same function..That is to allow the stator to freewheel at speed, allowing the maximum window area for the oil coming out of the turbine to be picked up again at the pump center.
On a spragless , the stator will remain in the way , to a certain extent.
Only real difference is that the diode can't possible slip, or fail to hold, due to it's design.
Any possible differences might be seen there.
Otherwise , I doubt you could ever pinpoint the difference in performance, between the two designs.`