Set the required CPU voltage. Start high to reach your stable target frequency and then decrease it gradually. Remember more voltage = more heat, so you ideally want to find the lowest voltage at which your CPU can run 4.5GHz stably.
1.25V is a good starting value that should be enough to get any i5-3570K to 4.5GHz, but this CPU was able to run stably at 1.21V. We’ll come back and adjust this down as needed later.
Hit F10 to save and restart your PC and boot to Windows. Fire up CPU-Z, Prime 95 and your monitoring software of choice (we’ve used AI Suite II, but be sure no to press any of the auto options otherwise it will attempt to reset the values).
Run Prime 95’s small FFT test. Leave this running in the background whilst performing some simple tasks such as web browsing. If your PC freezes, blue-screens or applications crash for no reason, return to the BIOS to tweak the voltage settings.
Be aware that with 1.25V and Extreme LLC CPU voltage will sometimes push the CPU to around 1.29V under load, and temperatures will rise accordingly too. Don’t worry, this is just the first part to make sure the chip can hit 4.5GHz.
1.25V and Extreme LLC should be more than enough for any i5-3570K (in fact, arguably too much, but we just wanted to make sure it would work), but if you encounter stability issues at this voltage, don’t increase the CPU voltage further. Instead, check your temperature readings, reduce the CPU multiplier down to 44x (4.4GHz) or perhaps reduce your memory frequency if it is above 1,333MHz.
Once you’re stable at your desired frequency, begin to gradually reduce the core voltage and LLC settings until you can reach a happy medium between stability, frequency and temperatures. There’s a great deal of variation between chips; one i5-3570K might be happy to reach 4.5GHz with 1.21V and Auto LLC, while another might require 1.25V and Ultra-high LLC. There’s no magic setting, but it’s easy enough to adjust the three required settings to find that sweet spot.
Somewhere between 1.21V with automatic load-line calibration and 1.25V with Ultra-high load line calibration, you’ll find a stable environment for your CPU to boost to 4.5GHz. As we’ve not adjusted any of the Intel C-states or Speed-step technology, the CPU will still clock down when idle, but boost to 4.5GHz when under load. These ‘frequency reducing at idle’ settings need to be disabled for even higher overclocks as they can affect stability. Be aware that overclocking dramatically increases power consumption; our test system here went from a system power consumption of 117W at stock to 155W when overclocked to 4.5GHz, so be sure your power supply is capable of handling the extra load.
With any additional change, repeat the Prime 95 test to ensure stability. An hour of prime 95 without issue is generally a sign of a stable overclock.
A word on temperatures: The integrated heat spreader on Intel Core 3xxx series CPUs is relatively poor at dispersing overclocked heat versus the previous generation, so they can run hotter under the same overclock than their respectively older Core 2xxx series brothers. With this 4.5GHz overclock and our modest Intel CPU cooler and with a CPU voltage of just 1.25V, temperatures remained below 85°C. However, turning LLC to maximum increases this to 1.29V under load, which causes temps to jump to around 95°C in a 21°C ambient. This is 10°C below the 105°C at which your CPU will automatically clock itself down, so if your CPU does need that much voltage to hit 4.5GHz, definitely consider a bigger cooler!