If your games are cpu limited, then faster single thread core speeds will help.
Such games typically are sims, strategy and mmo.
For fast action shooters, the graphics card is all important.
What is your graphics card?
What is your cooler.
How high you can oc haswell is determined by your luck in getting a good chip.
See how high you can OC keeping the vcore to a maximum of 1.3v.
If you can't get there because of temperatures in the 85c. range, then a better cooler will help.
If you do not care about money, a I7-4790K is as good as you can do with your motherboard.
For a marginal improvement, you can buy I5-6600K or I7-6700K with an overclock.
That is absolutely the best gaming cpu available today.
Likely the difference is not much worth it.
cpu vs. gpu... how to tell:
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, limit the maximum cpu% to something like 80%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
This will simulate what a lack of cpu power will do.
Conversely what a 20% improvement in core speed might do.