Some CPUs are better overclockers than others, and there's no way to tell without testing them. When you buy a CPU, you might get a good overclocker or a bad one. This is often called the "silicon lottery". You're a winner if your chip overclocks well, you've lost if you can barely get past stock clocks. These guys buy a bunch of CPUs and manually test them to see how far they can go while staying stable and cool. Then they sell the good overclockers for very high prices, and the bad ones for slightly cheaper than the base price. If you buy, say, a 4690K rated for 4.8 GHz, you can be sure it will be stable at that clock speed. It will probably cost you somewhere around $400 which is a whole lot more to pay, so IMO it's not worth it unless you're very serious on overclocking. And hey, who knows, you might get a great overclocker straight from Intel for the base price.