For a system using a single GeForce GTX 660 (non-Ti) graphics card NVIDIA specifies a minimum of a 450 Watt or greater power supply that has a maximum combined +12 Volt continuous current rating of 24 Amps or greater and that has at least one 6-pin PCI Express supplementary power connector.
For a system using two GeForce GTX 660 (non-Ti) graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 600 Watt or greater power supply that has a maximum combined +12 Volt continuous current rating of 36 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the critical factor.
Overclocking of the CPU and/or GPU(s) will require an additional increase to the 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 you are trying to achieve.
The Corsair Professional Series HX750W ( SKU# 75-001218 / CP-9020031 ), with its maximum combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is way more than sufficient to power your system configuration with a single GeForce GTX 660 (non-Ti) graphics card. It is also way more than sufficient to power your system configuration with two GeForce GTX 660 (non-Ti) graphics cards in 2-way SLI mode.
A good 450W PSU would be sufficient since you can't use two graphics cards in 2-way SLI on that motherboard anyway.