I've just done this - went from a 2017 Model S P100D to a Model 3 Performance
It's... different. Not necessarily worse, but very very different. Here's my initial impressions after a week.
- I The 3 feels a bit more like a toy car. It's smaller, and the centre screen is weirdly tiny.
- I don't like how the indicators don't actually click and stay in position when you indicate left/right. Seems weird.
- I took a wrong turn back from the service centre because the navigation is super different. I loved having the nav in the IC - just glance down and you see that cool 3D view of the road and it's right there... having to properly look over to the main google maps screen feels quite awkward to me
- It's fast... the P100D was insane, of course, but the Model 3P is about as responsive in daily driving
- Using the drive stalk for autopilot is also quite weird... it's less "seamless" than the dedicated little stick you get in the S
- I will miss my free supercharging, though I never really used it
- I will miss having free premium connectivity for life
- Autopilot is much better on the 3 than the P.
- The size is much more suited to the city I live in.
- It's actually quieter (road-noise) wise than the 2017 S and smoother.
- The boot is weird. I miss not having the powered boot and the huge hatch and parcel shelf and so on.
- The door handles are a bit weird. Initial impression is that people can't figure them out and you do have to show them,
- The phone key is less reliable than the fob. The "walkaway lock" feature was something I never worried about in my S, but already the 3 has failed to lock on me. Check your car, manually lock it, or get the fob
- I didn't get the FSD package. It makes no sense in the UK.
- The interior finish is so, so spartan. Really basic, nothing much to talk about there.
- It is much smaller, which is generally a good thing.
The Model 3P was 1/3rd the price of the P100D (when originally bought). You can definitely tell.
Biggest thing for me is that I miss having that instrument cluster display for navigation and "stuff".
If I were you, if money isn't much of an issue... I'd update the AP computer and the MCU, and stick with the S. Or, get a new S.They've also got a lot cheaper and better since 2017. If I were doing this over, I'd go for a long range S.