What refresh rate is your monitor? if it's 60hz, there is no point aiming over 60FPS aside from consistency.
The easiest way is to just test for yourself, as there are many variables you haven't describe which creates the scenario correctly answered.
Decrease the resolution as low as you can. Just make sure the GPU usage when recorded by a program like MSI afterburner isn't near 99 - 100%, and atleast one of the CPU's cores is. The FPS you receive there is your CPU's performance limit. If it still produces undesirable framerates, you can only upgrade the CPU. If the FPS produced there is fine with you, the CPU is fine and it's the GPUs problem. If this is the case you just have to turn down graphics settings + resolution.