Upgrade your cpu. A GTX 980 cost as much as an i5, a motherboard and a new case. Not only will you feel like you have a new computer but you'll alleviate any performance issues cpu wise that you currently have.
You have to ask yourself if you really want to wing it and cause bottlenecks, stuttering and the like. Overclocking won't help, you'll get 1.5GHz at most which won't even compare to getting a fresh intel cpu. You need to create a stable foundation, and you realize now that you'll have to pay for it in order to get what you should have right now. So upgrade your cpu now and then get a graphics card okay! Have a nice day.