Hello. Thanks for all great info in this thread.
I bought Z370 Taichi since Jan 2018 and have many experience to share with you.
First many of you probably know. Z370 Taichi use ISL69138 as VRM controller so look for VR VOUT instead of Vcore.
Board can do 3866-3900 12-11-11-28-220-1T tight 2V+ with Panram Ninja-V 3000Mhz CL15-17-17-35 (low end B-die).
I expect 4000 or a bit higher on better memory kit like Galax HOF or TridentZ.
4133Mhz 17-18-18-38-350-2T 1.48V is best 24/7 result for this low end B-die kit.
LLC is great for 8700K but for 9900K it drop quiet large amount of voltage (looking at VR VOUT) I set 1.46V in BIOS but during Cinebench it drop to 1.385V.
I wish ASRock can improve LLC1 to match LV.7 ASUS and LLC2 to replace current LLC1.
Generic memory OC is very fun. I have Hynix OEM 2133Mhz RAM (dual ranks AFR) and it can OC to 3500Mhz 16-18-18-38-360-2T 1.38V (higher voltage didn't yield tighter timings or higher frequency for 24/7).
12-17-17-28-350-1T 1.9V is playable for short benching too.
Mixing memory chip is another great job for this board. Kingston Value RAM 2666Mhz that come with Hynix CFR and Micron D9VPP (E-die) together can achieve 3800Mhz 16-23-23-43-1T 1.48V
If that is not enough what about 4 dimm overclocking with 2x dual ranks AFR + 1x single rank CFR + 1x single rank Micron E-die ? 3200Mhz 13-19-19-37-2T 1.48V is another great results.
I have include Thaiphoon Burner / Asrock Timing Config / AIDA64 bandwidth test in the videos.
It is a shame that during 1.5 year I didn't play much with offset because I think it is full of bug like PC not wake up from sleep / idle freeze / not enough voltage under load.
But today I just carefully read this thread again. Several days ago I try -150mv till -40mv with LLC auto. Idle voltage is very high but too low volt under load. That is enough to cause WHEA in HWInfo64.
So today I try -120mv with LLC level 3. Everything seem good. Load voltage is what I like and idle voltage is low too (I enable all C-state / speed shift / speed step etc).
Another thing that I notice is with 8700K 300K VRM frequency (default value) is fine but 9900K at maximum 600K can yield better stability.
I read somewhere on Elmor post about ASUS 500K vs 800K and 800K give better results on undershoot / overshoot.
I wish Asrock can bring back 1M frequency like Z170 OC Formula.
I have custom loop and VRM temp can hit 90C under heavy load. Use small fan and it never exceed 63C even the in the hot day (33-34C ambient).
Something that I curious is about memory slot. As I said before My OEM Hynix can hit 3500 16-18-18-38 24/7 stable. But both stick when populate to slot A2 can hit 3800Mhz at the same timings. One stick is even boot at 3866 !!!
But when I try both on B2 they never exceed 3500 unless I relax primary timing to at least 19-21-21-41 (19-22 19-23 19-25 etc work also). But that doesn't make it stable. Best I can get is 3733 19-21-21-41 but got error with just Super PI run. Never mind memtest.
So slot B2 is weaker than A2 by 300Mhz with dual ranks AFR. Quiet huge.
But it work fine on 3800Mhz with single rank CFR and Micron E-die...
Thanks again for all great info.