Check
this out, and
this.
Key is high PCI-E freq and high IOH Core V.
You could say CPU PLL needs to be on sweet spot and I would agree. I use 1.35V for 980X, but for 970 I was using 1.2V. No way of finding it, but trial and error.
BTW, don't drop everything to lowest possible, just use known stable settings, and try to avoid lowest UnCore multi, very unstable for me.
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