Calculator gave me 407W - ??? Seems kind of low.
If I find a cheaper 600W, would that be enough?
I found that an i5-750 with an 5850 only used 400W even when lightly overclocked (3.3) so I would be prepared to expect a 600W to be plenty.
I ran 3x4870 in my i7 (3.8) system with a draw of just over 740W from the socket - and an 4870 is more power hungry than your system, and so's my cpu.