TL;DR version: I only drove the S6 and own a 2017 340i xDrive. The GTS handles far better than either one.
After driving my 2011 RX-8 R3 for 5 years, I wanted a different car that I can enjoy with may family of 5. The RX-8 was very reliable, but since I only put 23,000 miles on it or so, longevity was never tested. If I had only 2 kids, the back seats of the RX-8 would have fit a pair of average-sized adults fine for trips less than, say, 2 hours long. So yeah, I am fond of that car.
I drove an S6 (2017) first. The power was intoxicating. The interior was perfect. The craftsmanship was befitting the $80k price tag (Arras Red, Sports Package, Panther Black paint ... YUM). But, even after two test drives, I was left feeling like something was wrong with the steering. It was accurate, well-weighed, and adjustable. I just could not pull the trigger. Then I decided to branch out. Even though C&D gave a scathing review of the Lexus GS350 F Sport, MT was much kinder. I drove it. It was even more underwhelming. Perhaps Lexus wanted too much to impart a "sporty" feel, but it was not that quiet, it was not that comfortable, yet it was still numb. I actually bought a 340i the next day. The steering was about the same as the S6 -- very precise, very numb. However, it was actually quieter and more comfortable than the Lexus! And the 340 was way quicker. Since the one I tested came with a stick shift, AND (as a result of the stick shift?) the dealer gave me a huge discount (less than 100 miles on the odometer), its higher sticker (than the Lexus) came in under the (after discount) Lexus price. After driving it for a few months, I kind of got used to its steering, and just settled with (what I though was) the fact of life with modern luxury "sports" sedans. My frame of reference, in addition to the RX-8, were a 2009 (new then) 328i xDrive and numerous other Mazda cars. The RX-8 was one of the best electric steering setups. Considering it came out in 2003, it's amazing that a car that inexpensive had the electric steering figured out that early.
I don't like SUVs. But the Jaguar F Pace reviews were spectacular. The electric failures -- typical of Jags -- seemed equally spectacular in the reviews. Then Porsche Macan GTS came out. I did not care to be seen in a Porsche, so an SUV Porsche already had two strikes against it. However, the reviews were just so good! I drove one, then I bought one the next day. Its handling gave me hope again. I imagine the F Pace and Giulia QV are the only two that can rival the GTS in its combination of handling, power, and luxury features. The QV seems like it's failing left and right already. The fact that it left an MT editor stranded in the middle of the street (due to faulty start-stop system that failed to start again. OOPS!) left me so cold. Even a weekend toy should not leave you stranded these days! If you are thinking about cars like the S6, M3, etc, try the GTS too! It'll be one of the most fun luxury wagons you'll drive.