Is this a good PSU for this build?

Here is Guru3D's power supply recommendation:

GeForce GTX 680 - On your average system the card requires you to have a 550 Watt power supply unit.
GeForce GTX 680 SLI - On your average system the cards require you to have a 750 Watt power supply unit as minimum.

If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina.
Source: http://www.guru3d.com/articles_pages/geforce_gtx_680_review,9.html
PSU recommendations:



http://www.newegg.com/Product/Product.aspx?Item=N82E16817207017 ( 20% off w/ promo code XFXP20, ends 12/12 XFX PRO850W XXX Edition)
 
At those prices I'd go for the gold over the silver PSU.

You don't really need a monster/1kW PSU. The GTX680 is around a 200W card. So assuming you are running stock you only need to handle 200 * 2 + 100 + 50 = 550. A high quality 650 and most 750W units should be more then enough. Even less if you have a 77W CPU and not a 95/125W one.
 
The PSU are both built by Seasonic and the XFX has a 20% discount on top of already being cheaper 😉