Well it only has 2 pci-e connectors while you need 4.
But the 12v rail does have 408 Watts available which should be enough if you were to split them...
I would go for a PSU that comes with 4 pci-e connectors though, they are made to hold that kind of power and won't be maxed out all the time like this on would be.
can you recommend one that's decent quality and cheap?
i thought the radeon 6870 comes with an extra molex -> pci-e adapter though
thanks