IF you already have that PSU it's going to be fine you will have no issues trust me. Don't fork out money on a new PSU when the one you have is capable. yes CM Don't make the best quality psus afaik but it should be more than capable.
I have a similar PSU Ocz ModXstream 500W with similar Amp rating and have no issues running my AMD Phenom II x4 965 @ 3.8ghz & a 7850 2gb @ 1100/1250
what is the rest of your system?
The OCZ has reviews that it delivers what is promised and has 432watts available on the +12 volts. CM extreme power has troubled reviews and only has 360 watts available on the + 12 volts, so not really comparable.
Regardless the CM specs are sufficient to run HD7850 but it is it lack of quality and protection that is worrying.