The max TPD of a GTX 680 is around 200 watts or so.
But that's only if you're running it at stock clocks and voltages.
I prefer Nvidia's newest line of GPU's because of their very low power consumption and cool temperatures. AMD Radeon cards are power hogs and are prone to overheating.
I'm guessing that Nvidia learned their lesson with the catastrophically failed "Fermi" GTX 4xx series cards.