I suspect that you might be having an issue with your VRM keeping voltage stable.
I don't know that B chipsets have it, but if so increase your load line calibration up (towards/to) 1 and see if it will get stable.
In my own case I have a 2700x on an X370 Taichi. I cannot enable PBO and XMP at the same time regardless of what I have tried and remain stable in the windows enviro. Games like a champ. If I turn off PBO and manually set the timings just like XMP it runs full stable all week long. I am seeing less than 50mhz difference on or off and a mild temp difference for the reduced voltage.
Far from an OC expert, but you just might not have gotten the silicone lottery on your chip.
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I suspect that you might be having an issue with your VRM keeping voltage stable.
I don't know that B chipsets have it, but if so increase your load line calibration up (towards/to) 1 and see if it will get stable.
In my own case I have a 2700x on an X370 Taichi. I cannot enable PBO and XMP at the same time regardless of what I have tried and remain stable in the windows enviro. Games like a champ. If I turn off PBO and manually set the timings just like XMP it runs full stable all week long. I am seeing less than 50mhz difference on or off and a mild temp difference for the reduced voltage.
Far from an OC expert, but you just might not have gotten the silicone lottery on your chip.
i will try