Audi’s most powerful road car ever is going out of production by the end of the third quarter of this year.The RS6’s billing as Audi’s headline output act will be replaced by the R8 GT.Although the most focussed of all R8s is quicker it will remain 14kW down on the RS6’s 426kW output.As the RS6 fades off the performance car radar (following BMW’s recently retired E60 M5) fans of Ingolstadt’s bruising full-sized über-sedan will bid it a fond farewell.Despite being quite late to market (it only arrived in 2008) the RS6 mated a 426kW 5l turbocharged V10 to Audi’s rather unremarkable A6 underpinnings. Brand neutral observers thought Audi would be courting disaster by adding so much power to the A6 chassis. In the fullness of time RS6 proved to be a (very) well sorted performance sedan.The RS6’s epic pace was contained by Audi’s signature quattro all-wheel drive system, whilst adaptive dampers ensured a driving experience that could be varied between tolerable ride quality and apex-clipping poise.Perhaps the most curious consequence of the C6 RS6 was its status amongst aftermarket tuners. Nearly a dozen German tuners produces RS6 versions with power outputs exceeding 500kW.Legendary Audi tuner Roland Meyer's MTM RS6 Clubsport is claimed to be good for around 350km/h. It has all come to an end now. The second generation RS6 will always be remembered as the most powerful German über-sedan of its time.Audi’s new A6 is (finally) expected to debut at next year’s Geneva Auto Show. If the C6 RS6’s development timetable is anything to go buy, it will be quite some while yet before we see another large Ingolstadt über-sedan bearing the famous moniker.