Another 580? sli

[black-ops]

Okay - So finished my RIG,

Must say - love it.
2600k oc'd to 4.8 Ghz on a Corsair H60
8GB HyperX ram 9-9-9-24 DDR3
and ofc a gainward GTX 580.

I am thinking of popping another one of these badboys in my machine but i'm running of a modular XFX 850W PSU, will this be enough for SLI - it says SLI - certified etc, but not sure if another one of these will be okay with this PSU:

http://www.overclockers.co.uk/showproduct.php?prodid=GX-141-GW

It does say 244 Watts... so in theory I should be fine, right?

 

[Tediore]

850w will be fine for SLI 580s, providing it's of a decent efficiency rating. I believe the XFX higher end models had silver?