Seems like a Model S meets most of your needs and is more of a direct replacement for your A8 than a Model 3.
Yes, that is true however only at first glance.
The A8 is actually uncomfortably large on the Italian roads I started driving on recently (after getting a summer residence there). The roads are so narrow that people don't stop or anything if the side mirrors just touch lightly. (On that note it is also not optimal to drive a brand new car there).
Also, with quite a bit of driving on the German Autobahn, I am hoping for supercharging stations that support the Model 3's 180 kW charging capability, so I can sustain higher driving speeds there (see also
Time Optimized Traveling Speed: the Final Graph).
Lastly, I really need the long range for my frequent road trips and a Model S 100D is really quite expensive...
However, once I get the invitation to configure my Model 3 with known pricing incl. options, then I will also look at a used Model S 100D, to make sure I am making the best choice. A used model S with unlimited Supercharging could become appealing, for the right price.
Thanks for your feedback.
PS. I should add that I have driven my A8 a _lot_ at very high speeds (including overtaking the police with their blue emergency lights on, on the Autobahn), and I think I want to step down the very high speed driving, just a bit, before the statistics catch up with me. So the I am unsure about paying for the various performance upgrades.