Palit Radeon 4870 X2 CrossFire Video Card Review - Power Consumption and Final Thoughts - Legit Reviews
321w for a 4870x2.
I had a 600w stealth rma'd it and ocz sent the GXS 850w as a replacement. Theoretically it'll work but I wouldn't do it with the stealth.
You should fire off a pm to Skymtl and see what he has to suggest.
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x4 965BE 3.7ghz / Tuniq Tower 120/ xfire HD6870s / 4x2GB G.skill/ S12D 850w/ Ga Ma 790X-UD4/WD640AALS Black x2, WD1TB FALS x1, Seagate 250GB x1/ BenQ 21.5" 1920x1080/ Win 7 64