Long story short my Seasonic x660 bit the dust and died last night so im currently getting it rma'd.
I need a temporary replacement for the time being and the OCZ 500W ModXstream Pro is currently $35 (after mir) at my local re-seller.
I was running a 6950 on that PSU and the rest of my components were more power hungry than yours. Take a look at this review at Guru3d: http://www.guru3d.com/article/radeon-hd-6850-6870-revie...
278W power draw from the entire system with an aggressively OCd CPU....your sytem will run fine.