There might be a few still using such CPUs, but, most likely try to choose CPUs made a bit more recently...as in this decade, and, within the last 5 years is better yet, and, if AMD, at least a Ryzen 1400 or above...
The Core2 Extreme QX6700 is clocked a couple hundred MHz faster....which would obviously probably make it faster than the 6600...
However, I have seen videos showing these CPUs capable of 40 fps in many games, which, if acceptable, might suffice for some folks..
https://www.youtube.com/watch?v=oLTZmFhnu0E
https://www.youtube.com/watch?v=uQZ8meWUZcQ