I'm running dual GTX 460's with a i5 750 @ 4ghz on a XFX (seasonic) 750w and it hardly breaks a sweat. You'll be fine.
wa1 is correct, cooling will be your biggest issue. I had no issue when running a single monitor (36c idle/74c OCCT load), but when I'm running 2 monitors at different res and the second card idles at 48-49c and the load temps increase by around 10c. This is all in a Windtunnel (2 x 250mm, 3 x 120mm) with liquid on the cpu.
What amperage is your xfx (seasonic) 750w on 12v rail?