We measure system-wide power draw from the wall while running the 3DMark Time Spy stress test for 30 minutes.
We also use Nvidia PCAT to measure power draw of the graphics card only, with readings from both the PCIe slot and the PCIe power cables combined into a single figure. This provides us with significantly more accurate data to work with as it is measuring only the GPU power, and not total system power which is a fundamentally imprecise measurement.
As for power draw, the Gaming X Trio averaged 167W over my testing. That's fractionally lower than the Palit StormX OC, despite the MSI running at higher frequencies. 4W is hardly a significant difference, but perhaps the 7-phase VRM (compared to 5-phase on the Palit) is contributing slightly to MSI's increased efficiency.