Well, on rear it's possible to run lower ETs of course if you have enough camber adjusted.
I have -1°10' on all four wheels. So no need for lower ETs on rear.
Or you might not be fast enough.
I run 8x19 ET45 with 225/35 and 8x18 ET44 with 225/40 on a coilover.
I know several people runnung simmilar combinations.
It's
very close.
So I can not recommend ET37 both front and rear to anyone.