Corsair AX1200
Enermax Galaxy Evo 1250W

If you're really cash strapped an old Corsair HX1000.

Your 800W might work at stock everything but it'll be near capacity.

My system draws 850W at 100% load on everything. That's 722W DC at 85% efficiency. If yours is a few years old that may limit you to less than 800W as well.

When buying a PSU for 2x 580s I would never recommend anything under 1000 so you can use up to 800W DC and not worry about going over 80-85% capacity with a continuous load.

I have a cooler marster 1000w running 2 580s in sli. I had this from my old PC but if I to get a new one I will get the corsair ax1200. It's bit expensive but you get what you pay for.

kmconstable

Corsair or Antec 1200W units are great.

+1 on that antec 1200

mwparrish

Corsair AX1200
Enermax Galaxy Evo 1250W

If you're really cash strapped an old Corsair HX1000.

Your 800W might work at stock everything but it'll be near capacity.

My system draws 850W at 100% load on everything. That's 722W DC at 85% efficiency. If yours is a few years old that may limit you to less than 800W as well.

When buying a PSU for 2x 580s I would never recommend anything under 1000 so you can use up to 800W DC and not worry about going over 80-85% capacity with a continuous load.

My friend has a similar setup as yours, except that his CPU is a i7-920, and his PSU efficiency is only 80%  Draws 750W from the wall running Furmark, and factoring in the efficiency, system draw would be 600W.  Gotta love living in a 220V country. 

3xVicious

I have a similar question. Although I'm planning on running 2 GTX 580 3GB that EVGA is suppose to release next month in SLI. Will my XFX 750w Black Edition be able to handle the load? If not should I replace it with the 850w version or go with a 1000w? If I go with a 1000w, any good recommendations below $180? I heard good things about Corsair and Antec, but I'm not sure.

If you can afforod two 3GB 580s, why skimp on the PSU?  Get a high quality 1200W, and you'll have more room for future expansion, and overclokcing.

3xVicious

I have a similar question. Although I'm planning on running 2 GTX 580 3GB that EVGA is suppose to release next month in SLI. Will my XFX 750w Black Edition be able to handle the load? If not should I replace it with the 850w version or go with a 1000w? If I go with a 1000w, any good recommendations below $180? I heard good things about Corsair and Antec, but I'm not sure.

 
I wouldn't settle less than 850W, some people might recommend you otherwise like going with a 1000W just to be safe but all you need is a quality 850W and you're good with GTX 580 SLI. I just ordered the AX850W for my upcoming build and I'll be running GTX 580 SLI as well, I'm not looking to OC my cards so I know I'll be good. If you wanna go with a 1000W unit with that price then you should look into the Silverstone ST1000-P, it just doesn't have an on/off switch but if you can live with that then it's definitely a decent choice.

Quality 850W unit will do you fine for SLI'd 580's.  You can grab a 1000W if you want.  While 1200W is overkill, it won't hurt anything other than your pocketbook.  I recommend staying away from dual source +12V designs like the HX1000.

As many have mentioned, a quality 850W unit is all that is really needed to have a stable system with decent overclocking all around. The only reason you'd want to go with a higher-powered unit is if you forsee yourself adding a third card for Tri-SLI due to using Surround Vision or upgrading to at least a 2560x1600 display in the near future.
 
Otherwise, you're better off saving the extra money for something else.

SirWaWa

3xVicious

I have a similar question. Although I'm planning on running 2 GTX 580 3GB that EVGA is suppose to release next month in SLI. Will my XFX 750w Black Edition be able to handle the load? If not should I replace it with the 850w version or go with a 1000w? If I go with a 1000w, any good recommendations below $180? I heard good things about Corsair and Antec, but I'm not sure.

next month? how do u know?

He doesn't know..

It's worth reminding everyone that when it comes to electrical power, you should avoid continuously loading a circuit above 80% of capacity. I can't stress this enough.
 
If two heavily OC'd GTX 580s with an i7 8xx CPU draw 850W AC which converts at 85% efficiency to 722W DC and the PSU is only rated for 840W on the +12v rail (as most 850W PSUs are), then you are going to loading it down in games or folding at 86% capacity for extended periods.
 
While 86% doesn't seems like an issue and the PSU can certainly handle it, here is what you have to consider. Above 80% load the capacitors, coils, etc. are subjected to greater stress and heat which hastens there eventual failure. Most 850W PSUs have a single +12v rail rated for something like 70A.
 
When you have you entire system drawing 60A (722W / 12v = 60A ) on a single rail, if something fails the over current protection isn't low enough to prevent catastrophic failure. Even the Corsair AX1200 doesn't even provide over current protection (it draws over 100A), just over/under voltage and short circuit protection.
 
What's the risk? At a minimum, with a direct short circuit, the PSU will likely detect the variation and terminate power delivery. But let's say, as can often be the case in these situations, it's not a full direct short circuit. Let's say it's a partial short and that means you could be drawing far more current than you need for far too long and as long as the voltage being delivered is within specs, the PSU will continue to juice it. If it occurs across wires too thin for the load, they can melt or worse, start fires as they overheat.
 
I'm not only referring to this potential inside your rig, but in the walls of your home. Most new US homes will trip the breaker above 120v/15a but that still assumes the electrical contractor used proper 14 gauge wire or larger. If the circuit is 120v/20a then 12 gauge should be used. If someone cut corners, you could easily start a fire in the rig or in your home. It's better to know than to risk it.
 
That's the worst case scenario. A more likely event would be that you nuke everything in your system: CPU, mobo, GPUs, HDDs, etc. Gone. Why? Well, you just didn't want to spend that extra $50-100 on a PSU with multi-rail over current protection. This is why I went with Enermax (or Antec's 1200W). My Enermax comes with 6 +12v rails rated each at 30-35A. It delivers the same 104A as the Corsair AX1200 but each rail has 30A over current protection to prevent major catastrophic failure. My 20-month old sleeps in the room next to my office. I'm not going to put his life at risk over $50-100 bucks, or anyone else's for that matter.
 
The best advice someone can give is if you can't afford the cost of good, clean power, ($50-100 more to protect $1500+) then you probably shouldn't be investing in thousands of dollars in high-end components. Not trying to be harsh, just encouraging what is most responsible.

Good post Parish, actually making me read more into my PSU (kingwing Mach-1 1Kw)

A quality 750w or 850w would run 2 580s even oc. I ran 2 580s @900 core with an i7 920 @ 3.8ghz and water cooling on a tx750w. It gets hot but it ran for 3 weeks no pro untill I switched out for a 1200w. Would I recommend it? No not really but you will get by

2x GTX 580s... Bi-winning!

EarlZ

Im planning to run 580 SLI's in the next couple of months but if a 1200PSU is an absolute must then that idea is out of the window as I need to spend a few more for a new monitor, so I guess ill stay with a 1680x1050 monitor and enjoy a single 580 :D

 
1200W isn't a necessity... 900W continuous w/ 75A on the +12v is the ideal minimum, full load on system = 80% of PSU capacity.

 1000W PSU is plenty for SLI 580's. Just get a good quality PSU.