A game will be limited either by the cpu or the graphics card.
As a rule, the graphics card will limit games more than the cpu.
By buying a strong graphics card, you will be able to use more eye candy or game at higher resolutions.
I think the suggestion for a GTX950 is a good one assuming it is a significant boost over your current card(what is it?)
If you are concerned,
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 more cpu limited.