What watts power supply should I get to be safe with this system ?

ravndal15

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Oct 4, 2012
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Ive heard gtx 580's require a bit of power . Currently 750 watts is what has been proposed but im thinking maybe I require more ? Am I right ? Or is this enough ? If not what should I get

16 gb memory . Not sure 1333 or 1600 yet
2x gtx 580 gigabyte overclocked editions
2TB WD/Seagate SATA 3.0 HDD
Not sure what the motherboard is but it will be able to support two gtx 580's
i7 4770K

This is the best information I can give at this stage . What PSU watts should I require ?