Research very well the costs of owning RS6. Go to Audiworld forums, as around, how much main parts would cost (it shares stuff with A6 so it's not as expensive as you might think) but main bits like brakes and pads and oil changes and tyres it uses, etc, get a ballpark figure. If you are OK with those - get RS6, that car is insane. It is a bit boring to ddrive on limit according to most accounts since there is no drama to it, just brutal bullet train power. If thats what you like, and not happy oversteer you get with bimmer - buy the Audi. I think nowadays is good time to buy cars like that. You only live once - if you want it - and it seems you really do - get it. So waht if it turns into expensive disaster with costs, at least you'd have owned one.
Give the voice of reason a cup of Shut the Fack up and buy the Audi.
'07 TiAg E86 Z4 Coupe 3.0si