So many variables at play.
@JimShaw First, since your M3P came with the PZ4 it also probably came with the Uberturbine wheels, which are 20x9". The 235 tire width is visibly stretched on 9" wide wheels. I don't like that pairing and I don't know why Tesla did it. For that reason alone I would lean towards 245/35R20 or even 255/35R20. (Note, from what I've read some tires don't quite fit in 255/34R20, but many do, it is a close fit. 245/35R20 should be safe with any tire.)
However, since you seem to highly value quietness, be aware that you won't find any Tesla spec foam lined tires in 245/35R20 or in 255/35R20. You will need to stay with 235s for that on a Model 3.
Also, I've read that the Tesla spec 235/35R20 PS4S has a wider tread width than most 235s, plus the whole tire construction appears wider than the OE PZ4. Some people think the Tesla spec 235/35R20 PS4S is better than the regular 245/35R20 PS4S. I have no experience with either, I'm just passing on something I've read here.
Yes 245/35 should have slightly more sidewall than 235/35 with all the implications you described. The difference is pretty small though, I doubt you or I would notice even back-to-back with the same tire model, but in theory 245/35 gives a tiny benefit in ride quality vs 235/35, plus the extra 10mm of treat width, which can benefit grip. I'm all for those benefits, I use 245/45R18 on my 18x8.5" wheels on my M3P (standard Model 3 18" size is 235/45R18). And yes in theory it will make your speedometer and odometer read slightly slower. I think that's a good thing too since our speedos read slightly fast from the factory, and well if the odometer counts a tiny bit slower, that's fine for you right?
To my knowledge Tesla has never stated whether the car can/will adjust its speedometer or odometer readings for different tire sizes. It
does have a wheel+tire selector for all of the official Tesla wheels pair with their factory tire fitments, which
could be used to adjust the speedometer and/or odometer calibration, but the owner's manual does not say that with any clarity.
As for PZ4 vs PS4S, you probably read my posts already, but I felt the PZ4 that came on my 2021 M3P were disappointing in grip for a 280 TW summer tire, and I didn't like how much they squealed in hard driving either. I didn't hate the PZ4, but they certainly didn't wow me and I didn't consider them when picking 245/45R18 summer tires for my 18x8.5" wheels. For that it came down to PS4S and Potenza Sport, and PS4S were on national backorder then, so Potenza Sport it was and they turned out to be a major upgrade over the PZ4. Much better grip dry and wet, and no more squealing. I haven't used the PS4S, but I would certainly pick it over the PZ4. My priorities might be different than yours though!
