We used the WattsUp? Pro meter in these tests. This allowed us to measure power use directly from the wall. This meter also uses a USB cable to connect to a computer and Logger Pro software to graph the readings while we run our tests.
To test total system power use, we used AIDA64 Stability test to load the CPU and then recorded the results.
With dual-socket systems, power use can be rather high when fully loaded. The Z9PE-D8 WS did peak out at 422 watts, but keep in mind we had the system set to max performance.