Cheap PSU (2x 5850's) EDIT

[Monetizer]

So, I have bought myself 2x 5850's and I was wondering if one of these would do: http://www.gigabyte.com.au/products/product-page.aspx?pid=2796#kf (I know it's pushing it if at all but I have one on hand)

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[baka]

Even a 450W Seasonic G series/Rosewill Capstone 450 will do, but for peace of mind get the 550W version.

[Monetizer]

Even a 450W Seasonic G series/Rosewill Capstone 450 will do, but for peace of mind get the 550W version.

Would this work? http://www.ebay.com/itm/SeaSonic-SS-550HT-80plus-550W-ATX12V-EPS12V-Active-PFC-Power-Supply-for-Gaming-/251258747734?pt=PCA_UPS&hash=item3a80303b56&_uhb=1

[baka]

It's a little dated but it should be enough for a 5970.

[SirMintALot]

You can calculate the needed size of a PSU with http://extreme.outervision.com/psucalculatorlite.jsp

But remember: You want to run the PSU at 50% load to save energy. So if your PC needs 300 Watt, go with a 600 Watt PSU, especially if it's not a 80plus certified PSU. If you can go for a 80plus platinum PSU.

[baka]

You can calculate the needed size of a PSU with http://extreme.outervision.com/psucalculatorlite.jsp

But remember: You want to run the PSU at 50% load to save energy. So if your PC needs 300 Watt, go with a 600 Watt PSU, especially if it's not a 80plus certified PSU. If you can go for a 80plus platinum PSU.

Efficiency drops by 4-5% at 100% load compared to 50% load, it's not worth paying extra for a 700W bronze unit just to run it at 50% load.

[Monetizer]

Would a Corsair TX850 Enthusiast Series V2 be to overkill? (I might add another GPU later)

[baka]

Would a Corsair TX850 Enthusiast Series V2 be to overkill? (I might add another GPU later)

For the same money you can get a Superflower 800W Golden Green, or Coolermaster Silent Pro Gold 800w.

[SirMintALot]

You can calculate the needed size of a PSU with http://extreme.outervision.com/psucalculatorlite.jsp

But remember: You want to run the PSU at 50% load to save energy. So if your PC needs 300 Watt, go with a 600 Watt PSU, especially if it's not a 80plus certified PSU. If you can go for a 80plus platinum PSU.

Efficiency drops by 4-5% at 100% load compared to 50% load, it's not worth paying extra for a 700W bronze unit just to run it at 50% load.

That is true for 80plus PSUs, a cheap noncertified cpu will run at 55 - 60% efficiency. Let's say your computer needs 300 Watt. The cheap PSU will pull 545 watt (at 100% load and 55% effiecency) from the socket, while a 80plus platinum PSU will only pull 319 Watt (at 50% load and 94% efficiency). If you run both 24/7 for a year then the differency per year is 1974.34 kW/h. Here in germany where we pay around €0.26 (about $0.19) per kW/h, so a platinum PSU saves me €513,32 (about $375,12) per year over a cheap PSU at full load. From that money I could buy 2 more platinum PSUs.

[Monetizer]

Is it ok to buy them used of Ebay or is that a no no?

[baka]

Is it ok to buy them used of Ebay or is that a no no?

If it has 2-3 years of warranty left on it, I'd say go for it.

[Monetizer]

Updated OP