MERCEDES-BENZ has arrested the credibility slide that saw its initially popular M-class SUV slipping out of contention in the Australian prestige market. And how. The new M-class storms into Australia with more of everything, immediately slotting into place as a topline alternative in an increasingly crowded category. The ML320 CDI version adds to the new vehicle’s extra space, greatly improved dynamics and sheer on-road presence with what could be the best diesel-fired powerplant available. We’ve said it before, but turbo-diesel engines are getting so good these days that the line separating them from petrol engines is finer than ever. And no more so than in this new, all-alloy Benz V6, which really does make you wonder why you’d bother with a petrol-powered M-class.