http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-770/specifications
Thermal and Power Specs:
98 C= Maximum GPU Temperature (in C)
230 W = Graphics Card Power (W)
600 W = Minimum Recommended System Power (W)
One 8-pin and one 6-pin = Supplementary Power Connectors
So 600 Watts works for one card 830 for two according to nVidia.
If heavily overclocking your system, I'd look at the Corsair HX series (except for the 10000 / 1050) and Seasonic X Series.
For moderate OC's, the Seasonic M series, Corsair TX V2 series, XFX Core Edition, Antec HCG / HCP series.
The EVGA 770 SC is a reference card with reference PCB and stock VRM. For that reason, you might want to look at the factory overclocked cars from MSI and Gigabyte which offer more speed from higher clocks as well as Custom PCBs with beefier VRMs. Can't see paying more money for a card with reference PCB / VRM when the competitions offers more performance and durability for less money. The MSI is $30 cheaper, 26 MHz faster outta the box and more long term OC Headroom due to the more robust design.
$349 EVGA SC 1111 core speed
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130921
$339 Gigabyte 1137 core speed
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125463
$319 MSI 1137 Core Speed
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127741