I don't have your chip, I do have an AMD chip in a system, but it's in my closet, I don't use it. All that being said, Overclocking is not an exact science, as your question seems to imply. It's a crapshoot, based on how good of a chip you got, when you purchased it. Some 6400ks might reach 4.5, some might reach higher, some won't get to that. Like a lot of things, there's a bell curve, or an area in the middle that the vast majority of chips fall into, with an ever smaller number reaching much higher, and conversely an ever smaller number reaching much less.
The following is a general set of over clocking principles. First thing, take control of your core voltage, meaning take it off of automatic and put it in manual mode. Then start slowly adding clock speed and doing system stability checks. Keep saving your results, so long as the system passes stress tests. When it fails, you have to decide if you're comfortable with the temps, voltage, and clock speed. If you're comfy adding voltage, you can do that, until the system is stable again, or back off on your clock. Overclocking is all about balancing voltage, performance, and temperature.