I've owned a 2006 rs4 for 3 years now and it's been brilliant. Never skipped a beat never used oil, great on a daily commute and motorway journeys done about 35,000 all in all. Not even that bad on fuel all things considered, gets mid 20s day to day. The carbon buildup is an issue but it's not something you can do anything about sort of getting it stripped and cleared out. Mine went on several dyno days (mainly to just to have a giggle and out shout the teens with the fart cannons [emoji4]) and the average seemed to be around the 380bhp mark. Mine has 95,000 on the clock now but a mate has a low miler (around the 30,000 area) and his is running about the same 380bhp going off a couple of dynos. Great cars to live with just be prepared for expensive service items like brakes and tyres