RC:
SciFrog:

On the segment of the turbo and turbo S, FF 612 Rapide, also the Bentley is probably close enough in term of emotions (not sportier, different).

On the lower segment? Cayenne and Macan and some Audis/Mercedes SUVs are close enough and much more practical and way cheaper, and the Tesla Model S is so innovative it doesn't matter if it is not as sporty with its massive torque. RC seems to say the RS6 is also better...

The RS6 Performance is quite amazing and in Germany, you can get it with the 705 hp (and more...) ABT tuning and full factory warranty. Even for leases through official Audi dealerships, which is quite amazing. Audi Sport also offers the Akrapovic exhaust as an option, a bit on the expensive side (9k) but you don't loose your warranty.

I don't think that you can compare the RS6 with a Tesla S, despite the powerful (electric) engine of the Tesla. The Tesla weights a bit more than the RS6 and the chassis is...how to put it...not exactly the sportiest. Of course if fuel economy is your major concern, the RS6 is the wrong car.

In the USA many people in that segment will associate sportiness with acceleration, and the Tesla S will hold its own. Plus it is cool. The market share the Tesla S has in the luxury sedan segment is staggering for such a new company with somewhat lower interior quality.