Here's some things to look over.
First, make sure that you have your CCC settings correct. Specifically, go to Gaming Performance > Standard 3D Settings. Check "Use custom settings." This will allow the software to control the video card for optimal settings. You might also want to peruse the rest of CCC to make sure all of that is okay as well.
Second, generally, a 4500 series card is only slightly slower than a 5500 series card. I just want to let you know that the graphics card difference you have might be minimal (but I am definitely not saying that you should be seeing some more improvements because of the rest of your computer's upgrades.)
Third, which ties on to #2, is that you may be reaching some bottlenecking with your video card (though I'm not positive here). Bottlenecking is the term used when one particular component in your PC is limiting the power of the rest. While bottlenecking exists in everyone's computer (there's always a limit somewhere), it's always good to limit the bottlenecking. In your case, and in my opinion, the graphics card you have chosen is sub-par to the rest of your components. You might want to upgrade the video card to something a little more fitting for the rest of your components.
Lastly, I recommend reading up this "Low FPS" guide. You might find some other options to choose.
http://www.mmo-champion.com/threads/...FPS-Check-Here!
Hope some of this helps
Good luck!
EDIT: Also, for your particular CPU, your Config.wtf setting for processAffinityMask should be: SET processAffinityMask "15"
I recommend editing the Config.wtf file (WoW > WTF > Config.wtf) and finding this line. If it is not shown, add it on a new line. If it is, let me know what the value is. See
http://www.wowpedia.org/CVar_processAffinityMask for more information/details.