For a system using two GeForce GTX 780 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 850 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 60 Amps or greater and that has at least two 6-pin and two 8-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.
Overclocking of the CPU and/or GPU(s) may require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.
Are you looking for an air CPU cooler or a closed liquid loop CPU cooler?