mapping Intel XTU to BIOS settings for undervolting Coffee Lake on ASUS Prime Z370-A

[menaquinone]

Hi. I'm attempting to undervolt my Coffee Lake CPU Intel Core i7-8700K (8th generation) which is on the ASUS Prime Z370-A motherboard on Windows 7 (I bought this configuration thanks to info I've seen on phoronix) and I was wondering how to transfer the settings from Intel® Extreme Tuning Utility (aka Intel® XTU) to the ASUS BIOS settings...

More specifically, in my case, I'm mainly interested in two Intel XTU settings, how they map to ASUS BIOS settings(for Prime Z370-A):
1) Core Voltage Offset (in Intel XTU) which when changed also changes in tandem the setting Cache Voltage Offset
and
2) Processor Graphics Voltage Offset which also changes Processor Graphics Media Voltage Offset

In my tries, it seems as if the following mapping is NOT quite accurate:
1) Core Voltage Offset and Cache Voltage Offset (in Intel XTU) -> mapping to -> CPU Core/Cache Voltage - Offset Mode (in BIOS settings)
and
2) Processor Graphics Voltage Offset and Processor Graphics Media Voltage Offset -> mapping to -> CPU Graphics Voltage - Offset Mode (in BIOS settings)
The reason I say that it's not, is because I get 3-4 degrees Celsius higher temperature with the BIOS settings than with the Intel XTU settings. Also, the Wattage draw at the socket is 14 Watt higher with the BIOS settings.

My guess is, that I'm missing some setting which also needs to be offset lower. Or, simply Intel XTU is using different ways of applying offset which affects more components that way (seen by looking at CPU HWMonitor's IA Offset, GT Offset and LLC/Ring Offset which are modified by Intel XTU but not by BIOS's offset settings)

Let me show some screenshots to ease this.

Here are Intel XTU and BIOS settings when I'm using ONLY Intel XTU to undervolt:
In idle:










HWMonitor in idle:

Here's how it looks like in load:


(that's 190W constant consumption at the socket, this way with Intel XTU settings)


Here are Intel XTU and BIOS settings when I'm using ONLY BIOS settings to undervolt(thus Intel XTU settings are reset to their defaults to not interfere):

in BIOS (compared to previous BIOS screenshots from above) this is what's changed(note: I did reboot once with this changes so that 0.912V will be in effect and thus detected correctly):

here's idle:

I can't attach more than 15 pics per post(due to forum rules, it seems), so the other two will be in next post.

Note that even though ASUS and Intel don't provide a graphics driver for Windows 7, I was able to successfully use win7_8th_i3_i5_Driver_2.0.rar which I've found on biostar's site. Apparently some code modifications had to be done (the .inf hacks were not working for me, found on other sites) and thus re-sign the drivers for them to actually not display Code 43(like the .inf hacks would do for me, for DEV id. 3E92)

I mention that because I thought that the graphics driver being installed was important in order to know for sure that my undervolt is stable, for example using PowerMax to run a graphics test while also Prime95 was running, to test both CPU and GPU at the same time and see they don't crash.