Quick answer: no.
There is no such thing as a bottleneck.
If you are upgrading your graphics card, a stronger card will always do better.
It is just a matter of how much better, and is the cost of the improvement worth it.
It also depends on your game and how cpu intensive it is.
BF3, for example plays well with modest cpu needs in single player, but in multiplayer, it bogs down witn a weak cpu.
To help clarify your options, run these two tests:
a) 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 cpu limited.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 50%.
This will simulate what a lack of cpu power will do.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
set to 50% and see how you do.
If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.
It is possible that both tests are positive, indicating that you have a well balanced system, and both cpu and gpu need to be upgraded to get better gaming FPS.