Yet it depends in scenario how the game is ulitlizing CPU and GPU, like lets take for example some simlation game, it calcualtes what is where moving and that stuff and uses more CPU because GPU (or graphicly) isnt demanding game.
i3 is good CPU because it has good single core perfomance.
If your CPU is 100% and GPU 60% in game that uses both CPU and GPU , for example ASCO your CPU is bottleneck but it will still run 60FPS soo there is no problem in that, but if it ran 30-40 and if you swapped for better CPU it will gain more FPS (this is my way how i see bottleneck).
Third part that can cause low FPS is HDD fragmentation (and that includes missing textures), which is when you delete, copy and move stuff across HDD and its not optimized (as it has inner and outer circle , inner faster read outer slower as the head has to move).
In short it depends how you set up game (vsync and other things, like details and MSAA and FX) and how it ulitlizes the cores of the CPU and GPU.
Sorry if im wrong.