There exists a League of Extraordinary Super Sedans, and few four-doors can claim to be members. The quiet assassin of the group is, undoubtedly, the 2015 Audi S8.
This is thanks to the pairing of its well appointed interior with a 520-horsepower twin-turbocharged V8 engine under the hood. You can blend in with the pack thanks to the subtle exterior styling or you can disappear into the horizon should you need to remove yourself from the company of other cars.
[Disclaimer: Audi loaned me the S8 for a week and included a tank of gas. If you have the means, I highly suggest picking one up… truly a fantastic machine.]