Here is a quote from Hilbert Hagedoorn @ The Guru of 3D:
Here is Guru3D's power supply recommendation:
GeForce GTX 560 Ti
On your average system the card requires you to have a 500 Watt power supply unit.
GeForce GTX 560 Ti in 2-way SLI
A second card requires you to add another ~175 Watts. You need a 700+ Watt power supply unit if you use it in a high-end system (800+ to a KiloWatt is recommended if you plan on any overclocking).
Which seems to conflict with the Tom's reference link you posted. Why the difference? Am I missing something?