Radeon HD 6670 1GB on 300 watt PSU

your psu is ok for hd 6670 but it will be good to get an psu of atleast 550w or 600w and upgrade graphics card to hd 6870 which will give u lot more better performance then hd 6670 and your cpu is also good for gaming so go with higher gpu for performance higher is better and for price cheaper is better way to go. 

for gpu this.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

for psu.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

or if u cant afford that much and your resolution is of 720p so it will be good to get hd 6670 for medium settings gaming.