THAT most rarefied of niches, the luxury ultra-performance wagon, has just seen one of its founding members, the Audi RS4 Avant, return with all the improvements accompanying the Ingolstadt brand’s ninth-generation family car, but with even more performance and agility than before. Aimed directly at the Mercedes-AMG C63 S Estate, the RS4 offers buyers the sort of low-slung versatility and coolness that no SUV can match, in a package that oozes obsessive quality and attention to detail. We’re glad for choices like this.