£17,500 does not buy a 2007/57 A5 3.0V6 quattro even at auction. E92 3 Series Coupes go back further, have more rear passenger and luggage room, offer the better drive and, because all BMWs are chain cam and not all Audis are, is the better long-term bet. But an M Coupe sits on big diameter wheels with expensive low profile tyres that destroy the steering feel and ride comfort and are vulnerable to potholes, yet offer no benefit apart from bling. Better an SE.