but, yeah, ideally you want only just enough power to each card. Core clocks that can solve/handle tasks fast enough but without drawing more power than needed and taking priority/forcing a lesser Memory Frequency or fluctuations in voltage.

I think you're just gonna have to experiment with different combinations, I just found that the Asus Strix 470 - and according to most forum posts - are similar to the RX480 in that the potential for undervolting and effectively having each card working 33% less hard while producing a similar result.

I also use my OS/PC actively on this PC that contains the 470 and 480 so temps/fan noise are ideal to keep low - the Nitro+ OC RX480 is like a god damn Learjet with the noise it makes, so I like to keep it happy by generating less heat from the 470, also.