Using the extreme psu calculator, using two hard drives, two optical drives, 5 fans, 4 slots of ram, 1 additional pci card, and the processor overclocked to 3.6Ghz with 1.5 volts(I really didn't know what you had, I just thought I'd overestimate.)
Then I did 100% TDP on processor and 100% system load. With 20% capacitor aging. And of course with your two cards. Oh, and I chose the highend motherboard.
It was 640Watts. And I'm pretty sure you have plenty of amps with that psu.