FRENCH cars do it. Volkswagen Group and Mercedes-Benz cars do it. And now BMWs do it, too. Performance turbo-diesels, that is. It’s all the rage. Of course, the Bavarian car-maker has been at it overseas for decades, but only recently has our fuel been low enough in sulphur for BMW to begin importation of its 1, 3 and 5 Series diesels. In early 2007, the smallest – the 120d – received a torquier, more economical engine in the mildly facelifted Series II. At around $50,000, it’s expensive. But is it worth the extra over the superb Ford Focus TDCi and VW Golf GT Sport TDI?