I managed to pass a 12-hour stress test with Prime95 (Blend mode), also I left the PC in idle overnight and there was zero problem (no blue screen).
Today I tried to change the windows power plan from high performance to balanced mode, and as I expected the CPU clock kept jumping between 800MHz and 5GHz, while the cache clock between 800MHz and 4.6GHz, and the vcore (as expected) was constant all the time, note that the cache clock always stays 300 MHz below the CPU clock:
1.2 GHz to 4.9GHz
(CPU clock) - (300 MHz) -> 900 MHz to 4.6 GHz
The problem is that if I leave the system in idle in balanced mode, after 5-10 minutes the system always crashes with the same BSOD, DRIVER_POWER_STATE_FAILURE.
It seems that if the CPU clocks are not constant the system becomes unstable, but I can't figure out why, especially since the voltages are constant!