WHILE BMW (with its next-generation X5, due here in April) and Audi (with its all-new Q7) attempt to be all things to all people with one model, Mercedes treads an entirely different luxury SUV path by offering two distinct off-road offerings. Take the second-generation M-class, stretch it lengthways to accommodate one of the best third-row seats available, fit the otherwise optional dual-range transmission as standard, then wrap it in a chunky new body and, hey presto, the result is the biggest, most capable and most luxurious off-roader ever produced by Mercedes-Benz. While it may come at a hefty price premium over the five-seater M-class, the GL-class combines, for the first time, seating for up to seven with serious off-road ability and unfettered luxury.