The reason for this is voltage is potential difference. IE it's the level of difference between two points. If you have a big voltage difference between the IMC and your RAM you will potentially cause a cpu destroying current between those two areas.... not a good idea.
Run P95 and see if that's stable. I've got a almost similar system to you and running 4.0 at 1.375 bios and if i'm not mistaken my imc is 1.225 and ram set to 1.6 bios.
My temps are pushing 80c on P95 with a H50 need lower temps.
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