Power supply question? 1000w EVGA SuperNOVA 80+ Platinum

Ok, so I am grabbing a new 1000w EVGA SuperNOVA 80+ Platinum as I am getting a 780 and plan on SLI'ng them later on. Now, I know 1000w is overkill, I like to have a little extra power available incase i want to switch things up.

Will it cost me more to run(electricity bill) my PC with my CM GX 650W Bronze than it would with the 1000w EVGA SuperNOVA 80+ Platinum? Obviously the 1000w is larger so will it draw more power? even though I will only be using around half of the rated wattage? I understand that at 50% load thats when PSU's are most efficient anyway, so will this help? Confused.
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  1. PSU will only have to deliver the power the components pull so with the same components they will pull the same from the wall if they have the same efficiency whether they are 650 or 1000watts.
    Here is an example for a CM 900watt 50-80% is where you want to be http://www.anandtech.com/show/2624/3
  2. The higher efficiency supply will cost less to run, but just marginally so. Power supplies are also not flat in their efficiency curve, generally peaking at about 60% of their capacity.

    If, for instance your machine actually draws 400 watts of power on the supplied side and the PSU is 85% efficient, it will draw about 470 watts from the wall. If that same machine was hooked up to a 90% efficient power supply it would instead draw about 445 watts from the wall instead. A savings of 25 watts.

    Assuming you run your machine full tilt like that for 4 hours a day, and your power is $0.12/kWh you would save 25 * 4 * 30 / 1000 = 3kWh per month, or 36 cents.

    The rating on the PSU will just dictate how much it is capable of supplying, it has nothing to do with how much your machine will use.
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