Test run your games at lower resolution and settings. That will take load off of the vga card.
If the FPS increases, you can conclude that your cpu is strong enough, and a stronger vga configuration will help.
If the fps does not change much, then your cpu is not strong enough to drive the vga card fast enough.
Conversely, keep the settings and resolution high, and limit your cpu. In windows set the maximum cpu utilization to 70% or some such number and observe your results.
If your FPS drops accordingly, it is a clue that it is your cpu that is limiting you.
Let us know the results.