XD I think I had just posted on another one of your forums with the same topic. The results posted about your GPU temps confirm my suspicion, your GPU is bottle necking your rig.
IMO if you’re going to upgrade ur GPU I suggest something from the 6870 series. While I am somewhat partial to them, as I own one myself.http://www.newegg.com/Product/Product.aspx?Item=N82E16814150561
The 550ti will get you to where you need to be but for 150.00 after rebate the 6870 offers the most bang for your buck.