Is a high-end CPU a real need for a gaming computer?

Conclusions

After testing the performance on six different modern games, maintaining a mainstream video card (GeForce GTX 750) and changing only the CPU, the conclusion was crystal clear. In two of those games, the four CPUs performed the same way. In other two games, the Core i7-4770K had the same performance of the Core i3-4150 (while the other CPUs has inferior performance), and, in two games, the Core i7-4770K showed a small advantage over the Core i3-4150.
So, it seems to be clear the, using an average video card, a mainstream CPU like the Core i3-4150 represents no “bottleneck” on most games, and a more expensive CPU like the Core i7-4770K brings zero or very little benefit to the framerate on most games. This is because the most important difference, nowadays, from a mainstream CPU to a high-end one is the number of available cores (or threads), and it is clear that most games do not use more than four threads. It has been clear when we tested the Core i7-5960X.
Now we can confirm something every computer expert always says: if you are building a gaming computer with a limited budget, it is better to buy a mainstream processor (using the saved bucks to buy a better video card) than spending it on an expensive CPU.
In some cases, even an entry-level CPU like the Pentium G3220, or an old processor like the Core 2 Quad Q8300, does the job just fine. However, if you are building a new computer for gaming, we do not recommend those options: in some games, you will lose performance; and probably, new titles will demand more processing power in the near future.
It is important to keep in mind that or conclusions can not be equally applicable on a computer with a high-end video card, where a mainstream CPU can represent a performance bottleneck. If is it the case, however, the user probably has a larger budget and do not even think about buying a basic or average CPU.