Would that be future proof? as in if i add extra memory or graphics cards will it keep being effective?
no you want a 750W for 2 670's nVidia itself recommend 500W for a single 670. http://www.nvidia.in/object/geforce-gtx-670-in.html#pdpContent=2
For testing conducted for SLI 670, the resulting system consumption for SLI is 433W of which 293W are attributed to the gpu cards.http://www.guru3d.com/article/geforce-gtx-670-2-and-3way-sli-review/4
All points out to 750W being more than enough.
Corsair 750TX V2http://www.newegg.com/Product/Product.aspx?Item=N82E16817139021
Seasonic made, 62 amps on the 12V, 3 yr warranty