CPU Overclocking Details
As on many other mainboards, you can overclock your computer safely and rather economically by turning on the Single Max Turbo Ratio option in the BIOS. In this case, the CPU frequency multiplier is always set at its maximum, which is normally used by the Intel Turbo Boost technology for low loads only. With our CPU, it means that the clock rate is always at 3.8 GHz instead of changing dynamically in a range of 3.6 to 3.8 GHz. You can overclock the CPU more by moving the appropriate slider in the BIOS Home section. One and the same CPU clock rate can be achieved by changing the frequency multiplier alone or by changing it together with the base clock rate. The mainboard automatically does the rest (adjusts the power limits and voltages, etc), so you only have to choose one of the variants offered.
Although the Intel Visual BIOS provides three ways of adjusting CPU voltage (offset mode, adaptive mode, a fixed value), it is increased in the offset mode during automatic overclocking. That is, a certain value is added to the default voltage level. We used to promote this volt-modding method as it allowed to keep all CPU-related power-saving technologies enabled. It is indeed a good and easy method for any CPUs, but not for LGA1150 ones. The voltage regulator integrated into the Haswell CPUs increases voltage too much at high loads in this case. If you change the CPU voltage in the offset mode, you can overclock but a little and with a huge increase in power consumption. Maximum CPU clock rates are not achievable at all due to extremely high voltage and temperature.
So can the Intel DZ87KLT-75K be overclocked in an energy-efficient way, without any voltage increase? Yes it can. But besides setting a required CPU frequency multiplier, you need to manually increase the power limits. Otherwise, the multiplier will be dropped at high loads. In fact, you had to do so on every mainboard in the past, but then all of them learned to automatically set up the power limits depending on the user-defined parameters. The Intel DZ87KLT-75K can correct the power limits, too, but only during automatic overclocking (as you’re moving the slider in the Home section). If you overclock manually, you have to correct them manually as well. That's not hard, but somewhat inconvenient.
Energy efficient overclocking is only possible if you don’t increase voltage. It will ensure higher performance and, despite the increased power consumption, you can expect long-term savings due to the reduced amount of energy spent for each computation. Energy efficient overclocking is going to be environment-friendly as we showed in our Power Consumption of Overclocked CPUs review. However, when we test mainboards, we want to check them out under different conditions and loads, so we choose what overclocking method ensures the highest results. Higher clock rates and voltages mean harsher test conditions and it is under such conditions that we can better see any flaws or problems in mainboard design. That’s why we overclock our CPU to 4.5 GHz in our mainboard reviews, fixing the voltage at 1.150 volts and using the XMP settings for our memory modules.
When we overclock by fixing the CPU voltage at a certain level, some of the power-saving technologies get disabled. The CPU's frequency multiplier is lowered at low loads but its voltage always remains high. Anyway, we stick to this overclocking for the duration of our tests, especially as it doesn't affect the computer's idle power draw much.
The results are almost the same as we had with other mainboards except for one difference. When loading the XMP profile, the mainboard set the memory timings at 9-11-11-31-1N whereas the others set them as 9-11-11-31-2N. We made sure our memory could work at such settings without any problems. The difference is insignificant and can hardly affect performance but it reminds us of the long-time downside of Intel's BIOS. Intel mainboards do not allow to correct individual memory timings. All of the timings are set by the mainboard automatically and cannot be changed, even if you load an XMP profile. And if you want to change something, you can easily set any memory frequency or any of the numerous timings. But in this case, you have to manually set up every parameter. You cannot change but one parameter, leaving the others at their defaults. Modern mainboards are generally free from this downside, but not Intel’s.