I think a gpu upgrade will be fine.
To satisfy yourself, Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely cpu limited.
If you upgrade, make it a significant jump or you might be disappointed.
I would look at a newer 28nm based card like a GTX660ti or 7770 at least.
These three cards cost pretty much the same where I buy.
Sappire HD 6870 1GB GDDR5
EVGA GTX550 Ti Superclocked 1GB GDDR5
Gigabyte GTX650 OC 2GB GDDR5 DX11
Sapphire HD 7770 GHZ Edition OC 1GB GDDR5
Which one out of the above will be my best choise?
Also, The GTX660 Non Ti/Ti are over my budget limit.
Dude, If I was you, I'd but a GTX 560 off newegg... it pretty much outperforms all of those and is really cheap, and the 660 Ti would be a GREAT buy too, but if you must buy from this select group, I suggest the GTX 550 Ti SC or the HD 6870. I'm pretty sure the HD 6870 is the fastest card on that list.