corsair is good too - but not as good as corsair's professional series
If you use a platinum certified power supply that is 90% efficient at full load 650 watts would be adequate. As long as you don't overclock the gpu .For a bronze certified power supply you would need 750 watts. 500 watts is all you need for one 6970 gpu.. So 650 watts with platinum certification should be more than enough. Most people do overkill on psu because either they overclock the gpu or they don't buy a platinum certified psu that gives off less heat and more electricity. Being cheap with something as important as a power supply is plain stupid.