Confirmed ... without mGPU voltage bump it is impossible to get CPU stable at 3500MHz and MEM at more than 1600MHz.

Let's summary:
- there is no NB voltage for 880G and 890GX because there is no NB! (OC Tuner is a lie)
- IGP works as NB so mGPU voltage is NB voltage
- there is no difference in OC capabilities if you bump NB voltage via OC tuner (OC Tuner is a lie)
- there is a big difference in OC capabilities with mGPU bumped a bit.