Depends on the game, the settings, gpu etc. In a game like skyrim with no mods, you'll barely see a difference, but add 100+ mods and you'll see a difference as those mods are scripted, pure cpu. Faster cpu will mean more mods without loosing fps. Other games you may see a difference depending on the gpu. If the gpu is strong enough to handle anything thrown at it, your fps will go up. But if the gpu is taxed it won't be much if any difference.
So it'll only really be something noticeable if you are at limits, if there's room to move then you are increasing performance thsts not used.