its more than enough, they overclocked it to 4.818, and didnt hit 600 yet. close but look at the test setup:
Nvidia GeForce GTX 590 3GB graphics card (GeForce driver 280.26 WHQL)
120GB Patriot Wildfire SSD
Enermax Revolution 85+ 1.05kW power supply
Asus Crosshair V Formula motherboard motherboard
Asus Maximus IV Gene-Z motherboard
Asus Sabertooth X58 motherboard
4/6GB (3 x 2GB) Corsair 1,600MHz DDR3 memory (CL9)
Thermaltake Frio CPU cooler for AMD processors; Be Quiet! Dark Rock Pro cooler for Intel LGA1155 processors and the Be Quiet! Dark Rock Advanced for Intel LGA1366 processors.
that gpu right there is a power hungry dual gpu. since you are only using a 560ti, its WAY more than enough.