A friend of mine, Eaulive, who's also a member here, and myself have purchased a pair of empty 4520 at the same time from the same guy. But we developped our systems in different ways.
I have a three way and Eaulive has a four way. The difference being he has a 12" B&C midbass and I can attest that it makes a huge difference in vocals and snares. Therefore I will also add a mid bass 12" front horn loaded cabs when I find good ones.