I am not saying you should not have gotten it, clearly you have your reasons and your happiness is all that matters!
I am assuming you are a car guy and know everything about these audi V8's in your car and the past RS4 and current RS5 but if you got yours used I would immediatly get a carbon cleaning of the valves. These things lose power like there is no tomorrow with carbon build up and even brand new seem to dyno quite low. So to keep the power at its best definetly get a carbon cleaning every 10-15k.
The S65 is just such a better engine I would have a very hard time going to an audi with that V8 only because it really does not make stated power and carbon build up is terrible. Even the new RS5 with "450hp" is putting down nowhere near that and is putting out 350 to the wheels. Something about those FSI 4.2 L V8's just don't seem to put out what they are rated
But I admit its the sweetest looking and sounding car so you definetly made a great choice given your criteria!