Just based on your listed system specs, your CPU is holding back your GPU. Since the two work together to bring you performance, generally one of them isn't working to it's full potential because it has to wait for the other to keep up(they like to keep in step). In your case I feel like it's the CPU that is holding you back.
I'll just give you the info you need to make an informed decision on your own. If you want to find out whether or not your CPU or GPU is holding back your performance, you would follow these steps...
Disclaimer: This is meant to be a guideline to show you how to isolate the culprit. You shouldn't overclock your system unless you are comfortable with it, have ample fans and airflow in your case, ect. This is just the methodology so you'll understand it. Step 1: Run a benchmark at your current(default) settings. I'd suggest something like 3DMark. Run the benchmark maybe 3-5 times and take an average of the scores.
Step 2: Slightly increase your CPU clock speed(.1 to .2 GHz at a time), run another batch of benchmarks for an average and compare to the previous scores.
Step 3: Repeat steps 1 and 2 until there is no discernible difference between scores.
Once you arrive at scores that are nearly identical, you have found the sweetspot for your GPU. The point at which your scores stop increasing with CPU adjustments is also the point at which your GPU has become the performance bottleneck. You're only as strong as your weakest link and in your case, I would point at the CPU.
You have a bunch of options here and I'll list them in the order they make sense to me(both logically and economically)...
1) Lower your settings.
You didn't really say whether or not you're looking for better performance in general or if you were looking for eye candy mode. If it's the former, consider lowering your resolution and scaling back your settings a bit. Striking a balance between quality and quantity is always a good thing and it's free
2) Overclock your CPU
If it's something you're comfortable doing then it's also going to be the most cost effective option. A case with good airflow and a decent CPU fan are well within your budget and while you might not leap into eye candy, the difference will be noticeable in more than just your gaming. FWIW my GTX 480 wanted 4.1ish GHz before it would top out. I'm not sure your CPU can push that high, but you would certainly get all you could out of your GPU this way.
3) Upgrade to a new CPU
This might also require upgrading your motherboard so it could possibly be as expensive as a GPU upgrade. I still like this option better than a GPU upgrade because you get your performance in other places than just gaming too.
4) Upgrade your GPU
I list this last for the same reason I went through the testing methodology. You're only as strong as your weakest link. If you overclock your CPU and your benchmark scores increase, your CPU is the bottleneck. It's gonna hold back your GTX 570, it's gonna hold back my GTX 980 and if you had money to burn, it would hold back a Titan Z.
Sorry for the rant, but if you made it through then you probably have all the info you need to make an informed decision if you haven't already.
tl;dr
If you put a Ferrari body onto a Ford Focus chassis, it's going to perform like a Ford Focus. A damn sexy Focus, but a Focus none the less