I'm not sure whether an Audi A6 qualifies as a midlife crisis car, not even the fabulous A8. Nor a big BMW.
Classic Jenson Interceptor?
Ferrari 456?
Modern Aston Martin?
Porche?
How about a wolf in sheeps clothing...
VW Golf R Estate. All the modern comforts with terrific speed and road holding (the police here don't chase a Golf R, they call for helicopter assistance). Double twin pipes are the only telltales