This should lead to the biggest net spends in either club's history, right?
Almost certainly. Real Madrid might go sign David De Gea and Paul Pogba, because why not? Atlético Madrid might go crazy and sign a half-dozen of the best prospects in the world, because why not? Who cares if they get a Financial Fair Play warning? They'll pass by tens of millions the next time around because they will have gone two windows without signing anyone.