PRACTICAL and potent aren't often spoken in the same breath when it comes to either supercars or station wagons. But the RS4, Audi's flagship performance car, is different. Watch in awe as mum smokes the "family Ferrari" at the lights, for in terms of sheer acceleration - and hauling the vehicle up from warp speed - this mother-of-all-A4s is outstanding. Though ride quality and rear seat accommodation let the side down, vehicle dynamics and interior versatility make it almost irresistible.