If you thought the Intel Core i7 6700K was a beefy CPU with its maximum turbo frequency of 4.2GHz, wait until you see the numbers that extreme overclockers are getting out of it.
The highest freqeuncy for this particular CPU is held by Hong Kong's Chi-Kui Lam, who managed to squeeze 7025.66MHz out of the Skylake. To do so, he used a lot of skill, and a whole lot of cooling: -321 degrees Fahrenheit's worth of liquid nitrogen to be precise. For the rest of the build he used an ASRock Z170 motherboard, 4GB of G.Skill DDR4 RAM, a 256GB Plextor hard drive with Windows XP Professional installed, and a 1,300W Antec power supply.
A couple of German overclockers, Der8auer and Dancop, came pretty close to that record recently using an Asus Maximus VIII Gene motherboard. They also impressively managed to increase the speed to over 7GHz, but fell just short of the record at 7007.85MHz, securing second place in the current rankings. This is the fastest speed for that specific motherboard and CPU combination however. Dancop also has a number of overclocking world records under his belt.
These are all readily available components; all you need to join in is some serious cooling hardware. Admittedly pouring liquid nitrogen into your PC on a regular basis isn't the most practical way to PC game, but someone's got to do it, right?