That PSU is a complete overkill. To spend $400 on that thing would be just like trowing money out your car window. A pair of ATI 4890 cards will run just fine on something 750w - 850w. You could spend half of that and have no issues.
Here is an 850w Corsair modular PSU for $200.
http://www.memoryexpress.com/Product...24569(ME).aspx