You need to delete the word bottleneck from your brain. It only refers to the slowest part of the PC with the task your doing and can change parts depending on the task within the same PC.
For a more logical outlook, your processor will struggle in most modern games that can utilize more than 2 cores, some games will be really bad where the games really require more than 2 cores, games that are more single core dependent and are more GPU dependent your GPU will be the problem.
So to sum it up their no answer to your question unless your playing 1 specific game.