A STATION wagon able to slug it out with the best of Europe's high-performance sedans? Hardly likely, you'd reckon. But Saab's 9-5 Aero Estate intends to have a go at determining whether it is possible to combine the benefits of a refined, practical station wagon with very rapid over-the-ground capabilities. The Aero Estate does a good job on both counts but also compromises on both. The reduced ground clearance means extra care must be taken when venturing off the bitumen, while the tougher suspension and powerful, vocal engine take some of the edge off the 9-5's inherent refinement. And it seems to suffer from more torque steer than 9-5 Aero sedans. But it retains the carrying ability of the regular Estates and much of the sedan version?s dynamics.