Armoredhound,
Some overclock higher than others, so there's no "formula". You might be able to reach only 4.2, or as high as 4.8, or anywhere between. It all depends on how good an overclocker your particular CPU sample is. No one can predict that. We can only say what is "typical" for an i5-2500K, which is roughly 4.5'ish to 4.6'ish. The only way to know is to go ahead and overclock it to see what
yours can reach.
No two processors are identical;
each is unique in voltage tolerance, thermal behavior and overclocking potential, which is often referred to as the "silicon lottery".
Overclocking is always limited by two factors; voltage and temperature.
For 2nd generation Sandy Bridge processors such as your 2500K, the maximum recommended Core voltage is 1.375, and the maximum recommended Core temperature is 80°C, so
you'll need a decent CPU cooler. Whatever highest
stable overclock you can achieve without exceeding 1.375 Vcore and 80°C will be the best overclock for your particular 2500K.
Although there are plenty of guides available on the Internet to help you, I suggest that you start here:
CT