ASIC Quality and Undervolting

In regards to AMD rx series gpus, how much do you factor in asic quality when undervolting (when using predefined core clock like 1150clock)?

I have been ignoring asic quality but it seems maybe I could undervolt my higher asic cards a bit more... so i'm wondering like what metric or how much further they can be undervolted...

Let's say a card with 70% asic is stable at 920mv... would a 80% be stable at 900mv? 880mv? Lower? How much does asic quality even matter for this?