TITANX.
Seriously, the stronger the card, the more eye candy you can use and the higher resolution you can use.
And, it depends on the game. Some are cpu limited and some are not.
There is always a limiting factor(AKA bottleneck)
My guess is that you could be reasonably balanced with a GTX960 or GTX970.
------------------------------------------------------------
To help clarify your CPU/GPU 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 more cpu limited.
b) Limit your cpu, either by reducing the OC, or, in windows power management...