hd 7950 is a great card to go with. but your psu is the builder series psu from corsair which has the efficiency of about 80% and the hd 7950 is a bit more power hungry than the hd 7850 also since you have overclocked the processor itself i believe it is better not to take that risk.
you can also choose the hd 7870 and overclock is like hell to get better performance and fps.
you can check out the power supply specs at: http://www.extreme.outervision.com/psucalculatorlite.jsp
do keep in mind the efficiency level too.