TechPowerUp measured the peak draw of a stock PowerColor HD 6870 X2 @ 245watts
I think a premium 850W PSU could handle the max load OK. And I think the more typical gaming load would be well within the capability of a 850W PSU.
On the other hand the maximum power draw (Furmark) was a hefty 353W and might be closer to the draw if you do something like a max OC on the GPUs.
700W for the GPUs alone? That premium 850W PSU is sounding a bit light for a 'worst case' scenario.
I would advice not going with 6870x2 crossfires as quad crossfire is not very good.
the performance gain isn't the best when scaled pass 2 cards and you'd only see a real performance increases in artificial benchmarks.
thanks for the feedback WR2.
So I'm going by the understanding I should
now start looking for a 950-1000 watt
I'm roughly calculating the OC on my cpu to draw around
130-150 @ 4.5 all cores unlocked (thinking of it as a X6 overclocked)
in addition to your calculation of 706W for the GPUs
bringing me over 850 already.. so if yeah definitely higher than 850.