there is no reason to get a 1,000 watt PSU to run ONE card; think quality 550 watts.HIS Radeon HD 7970 X Turbo edition review
Our test system is based on a power hungry Core i7 965 / X58 system.
Measured power consumption
System in IDLE = 176W
System Wattage with GPU in FULL Stress = 390W
Difference (GPU load) = 214W
Add average IDLE wattage ~10W
Subjective obtained GPU power consumption = ~ 224 Watts
Here is Guru3D's power supply recommendation:
Radeon HD 7970 - On your average system the card requires you to have a 550 Watt power supply unit.
Radeon HD 7970 Crossfire - On your average system the cards require you to have a 750 Watt power supply unit as minimum.
and the very next generation of AMD gpus are going to be out until early next year, so get it now.