Hmmmmm, many things to go for. If you want to buy then an s4 (old style) would do the job, as mentioned 2.7 bi-turbo so can shift and four wheel drive too. Very stealthy.
You could see if any A6 4.2 quattros are available, I don't think they are too ostentatious...
Either that or Subaru Legacy. They are ace cars (try one) and go like stink in the right guise!