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 Tomb Raider at 4k resolution and the synthetic stress test Furmark – recording both results.
The Maxwell architecture is extremely power efficient – seen before with the excellent GTX750 ti, which took all the power it needed from the PCI e slot.
The Asus GTX970 Strix OC demands just under 140 watts when under gaming load – compare this directly to the R9 290, which takes 225 watts under the same situation. AMD really are so far behind Nvidia when it comes to the architecture efficiency.