What do soft power tables do? I don't get why they're needed.
You can't change the voltage on states P0-P5 on the core or P0-P3 on the Memory without modifying the registry. In essence the tables don't give you any extra hashrate but lower the amperage draw of the card. You can save like 60W per card.
Most people don't understand that. They simply open AMD settings and bring the power settings down -20% and think they are running at max efficiency.. which they are absolutely not. Not even close.
I have made tables that are lower for those states and it made absolute no difference to power draw.
then you did it wrong
this is mine for example... 1448mhz/880mv gives me ~1401mhz@875mv
complete system with 4 vegas 690watts from the wall on cryptonight - stable

I am not so sure. Every Vega is different. I do not think many vegas would run at 800mv on HBM for a starters. You seem to be under the assumption that all silicon is the same. I have identical AIB vega 56's and there is big differences between them. Some can so 980MHz on HBM, others cannot go above 890MHz.
800mV here is not to the HBM2 memory. HBM2 memory has fixed voltage; 1.26V for Vega 56 and 1.36V for Vega 64.
Reference versions use the same Samsung memory. That's why reference Vega 56 can be bios modded (unlocked to 1.36V) and achieve 1100 Mhz frequencies like Vega 64. Also, Hynix HBM2 is inferior to Samsung's (till now).
Correct - The voltage you see there in overdrive and wattman isn't really HBM2 voltage. Not really sure what it is tied to.
Functionally, it works basically like a floor voltage for the gpu states. It's why people say you need to have gpu mV at or just above your p3 memory mV