How are You doing it?
Is there a method? For example one card at time, down by 10mV pro minute, find the point it crashes, up 50mV, done?
kind of that.
but if you use msi afterburner you can set core clock and memory blending all three.
say 1150 core
2200 memory
-60 mv
may be good for
a msi rx 480 8gb card red led gamer model
but not for a
asus rx 480 8gb dual white model.
and each and every card even if the same make and model can vary a bit.