i5 6600k vrm temperature

A VCore of 1.264 V is low. I run my 6600K at 4.6 GHz with VCore at 1.355 V and 4.7 GHz at VCore 1.41 V. Others can reach 4.6 GHz at VCore around 1.30 V and 4.7 GHz around 1.40 V.

For a large part the temperatures limit the maximum achievable clock frequency. Do not forget that power consumption and temperature increase linearly with clock frequency (GHz), but exponentially with voltage (VCore). So, investing in better cooling means better overclocking potential. The limit is ultimately not the VRM temp, or the VCore voltage, but the temperature (temp).

The temp to consider is not the VRM temp but the "Package" temp (the highest Core temp out of the 4 CPU cores) as reported in real time (for example) by CPUID HWMonitor (free app.). It needs to remain ideally below 80 C under heavy load such as when under heat stress with Prime95. I allow it to go slightly over that for a short period of time though, but only exceptionally. The mobo protects the CPU by shutting down the entire rig when its temp stays above 85 C for too long. So there is really nothing to worry about.

It's not enough to state that you can reach "4.4ghz at VCore 1.264 V" (many people can), it must also be "stable" (= solid) under heavy load while using load stressing apps like Prime95 for example (free - there are many others). Otherwise as soon as some performance is required, your rig will keep on crashing.

The VRM (Voltage Regulator Module) is the power delivery system (comprising a group of electronic components) of the CPU/GPU which converts the PSU’s 12V to whatever the CPU/GPU need – a high-quality voltage is best for stability overtime (not just a high voltage). The VRM components are located on the motherboard, usually around the CPU. The VRM "as logical unit" is made up of one (and rarely more than one) chip that is called the voltage controller, or "Pulse Width Modulator (PWM)" chip.

The role of the PWM chip is to govern the phase drivers and (undesirable) doublers, if present. The drivers and doublers are connected to the MOSFETs and they are all part of the power unit. The final section of the VRM is where the filtering and voltage smoothing is done. This is done through inductors (popularly called chokes) and capacitors. A single set of “drivers, MOSFETs, chokes and capacitors” (note that "doublers" are not in this list) make up a single phase of the VRM. The overall quality, or rating of a motherboard is often expressed by how many VRM phases it has (and preferably without phase doubling).

In the case of the CPU, the whole point of the voltage regulator (VRM) is to take 12 V from the 8-pin EPS connector and step it down to 1.2 V (the stock voltage for most Intel CPUs). And that is done by pulsing the current trough each phase of the VRM. The more pulses (i.e. phases and frequency) the smoother the resulting current is.

MOSFETs (Metal-Oxyde Semiconductor Field Effect Transistors) are basically tiny switches. MOSFETs are governed by a high-frequency signal that comes from the PWM unit. MOSFETs turn on and off rapidly, passing trough high current in short pulses. By combining these pulses in more VRM phases, and at a higher frequency, the current for the CPU/GPU will be more smooth and stable. But the higher the current, the hotter the MOSFET gets, and heat affects (degrades) the resistance of the semiconductor.

So, past a certain point (as it is usually the case when setting the CPU multiplier above 46 (4.6 GHz) for most i5 6600K chips), the efficiency drops significantly and the heat increase is no longer linear. From there it’s a never-ending loop that will only generate more heat faster and faster, and for diminishing corresponding gains in performance (see what is required already to go from just 4.6 to 4.7 GHz). The voltage conversion starts at the MOSFET. It is handling the biggest workload, hence the radiators (HSF). By the way, HSF = Heat Sink and Fan.

If the VRM temp is really a concern (although it shouldn't be), you can always fit it with its own fan directly blowing on it (there are threads dealing with this). Not having enough ventilation of the VRM is often an issue with water cooling because the two fans of the radiator are often taking care of just that, the radiator, and not much else. Air cooling in the other hand often gives a much better ventilation with more air circulating throughout the whole case, including over the chips of the VRM.To optimise this flow, I measure temps in my case with the following very useful device: https://www.ple.com.au/Products/610556/Generic-Infrared-Thermometer-with-Laser-Armpoint. Have a look here for the fans: https://postimg.org/image/3t7g3ljjt/

Have a look here for an idea (complete with coloured thermal pictures) of the VRM's importance in dissipating heat (and where it is located):
http://www.tweaktown.com/reviews/7401/gigabyte-z170xp-sli-intel-z170-motherboard-review/index10.html

Here is also an interesting temp guide from INTEL:
http://www.tomshardware.com/forum/id-1800828/intel-temperature-guide.html