I stopped using power play tables since 18+ drivers. overdriventool is enough to achieve full hashrate at 165W with vega 64 and modified vega 56.
clock: set to 1600, voltage set to 850mV
mem: set to 1100, voltage set to 860mV
real clock is 1400 to 1500 depending of the card ; real voltage: 885 mV; shown in GPUZ.
4 cards rig is at 700W, system uses roughly 35W
This sounds like you still need PPT. Assuming a proper setup w/ PPT, actual voltage has historically *always* been lower than set voltage by at least 7-15mv, due to droop. A higher actual voltage vs what you set is exactly what you would have seen in the past w/o PPT, because your <=P5 voltages were fixed, and higher than your P6/7. Only thing is, those lower state defaults were usually much higher than 900-ish mv, so something strange is going on.
Also, a drop from 1.6 GHz to 1.4-1.5 indicates you are significantly off on your power vs frequency settings. Your card is being throttled because it doesn't have enough power, and sooner or later that will lead to instability. You definitely want to minimize that difference between actual and set frequency, by either increasing power, or reducing frequency. In the past, I've found that a proper ratio is around 1500 +/- 25 MHz for 900 +/- 15 mv