No need...850w is enough by every review that has done 570 sli. The corsair ax850 is enough. Even the HX850 is good enough.
Apparently the ax 850 or the seasonic listed above is even good enough to run the 580's in sli as alot of people with evga run those psu with those cards
Take a look at that article. The full system wattage on 570 sli is 578watts on a stress load test with the 570's just pulling 410 watts. Even if your system for some reason requires you to pull 650 (higher than the review) watts on load you still would have a decent amount of head room. I doubt you will pull much higher if even the same as they run a powerful rig.
No need...850w is enough by every review that has done 570 sli. The corsair ax850 is enough. Even the HX850 is good enough.
Apparently the ax 850 or the seasonic listed above is even good enough to run the 580's in sli as alot of people with evga run those psu with those cards