The ASUS GTX670-DC2-2GD5 is the better performing card.
The price difference corresponds to the performance difference.
What is the brand and model of your power supply unit?
For a system using a single GeForce GTX 670 graphics card NVIDIA specifies a minimum of a 500 Watt or greater power supply that has a combined +12 Volt continuous current rating of 30 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) @ 45-50°C ambient temperature, is the most important factor.