THE third-generation XC70 builds on the reputation of earlier models by offering wagon versatility with a touch of all-terrain practicality, wrapped up in a luxurious, safe package. The MkIII XC70 adds another dimension, however, in the form of a turbo-diesel engine - for the first time in the XC70. The superbly finished new wagon is looking better value for money than before, too. Despite suspension built for comfort and not gold-medal handling, compared to the old car the new model begs the question: Unless you must have seven seats, is it really necessary to buy the XC70's bigger brother, the XC90?