To test power consumption today we are using a Keithley Integra unit and we measure power consumption from the VGA card inputs, not the system wide drain. We measure results while gaming in Crysis 2 and record the results.
Nvidia have been nailing power efficiency with their current generation of hardware and the GTX660 is no exception. The MSI GTX 660 OC Edition consumes around 110 watts when gaming and this rises to 128 watts when loaded with the synthetic stress test Furmark.