A truly Slytherin conversation indeed, with so much being said indirectly (at least toward the end) and yet at the same time understood perfectly.  I think it's safe to say that Severus won the exchange, since he planted seeds of doubt in Lucius's mind that turning Gideon's skull into a trophy was enough to convince Narcissa which one of them was really the better man -- and that doubt has robbed Lucius of both his complacency and his sense of triumph with one blow.  A truly masterful stroke.