The 7850 takes less then half as much electricity and is on par generally with a gtx 570. I would defo go with the 7850 anyday of the weak. Instead of having a power station sound, you will have a cool running stress on your psu gpu running and future proofing your computer. Nice efficient system with a 7850.
I am getting a Corsair 750w, because I want to be future proof for all the upcoming things. Power isn't a big deal to me. Thanks tho!