Hmm well I would look at 800 watt power supplies at least, maybe even 900 watts. Antec and Corsair make good PSU's look into them. And BTW, if you need to spend more on a good brand Power Supply, do it. The Power Supply is one place you NEVER want to skimp on.
I use Corsair HX850W with 80+ silver standard for 2 SLI and OC every single component I am able to do on my PC. This PSU is at the highest blowing out a comfortly summer brees air at the back even thus I have tried to fry it as much I ever can do with OC, the fan is soundless. All top-high-end product into the single circuit! Corsairs PSUs is always thought to transfer more W then what it is written on the spec, am sure my PSU can transfer up to 1000-1200W without complaining at all. Recommend you to buy a Corsair PSU with 80+ standard. Happy hunting!