My setup is in my signature. Im thinking of adding a second GTX 670 to it, as well as a corsair link. Im wondering if my 750 will be able to run all this, keeping in mind I also have a pci-e wifi adaptor and pci-e usb hub.
For a system using two reference clocked GeForce GTX 670 graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 700 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 45 Amps or greater and that has at least four 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 most important factor.
The Corsair HX Series HX750 Power Supply (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 two GeForce GTX 670 graphics cards in 2-way SLI mode.
There's more than enough spare capacity to handle any overclocking of the CPU and GPUs and your liquid cooling loop(s).