Also here's my M3P 20" vs 18" comparison summary. This is based on 100% stock 2021 suspension that I had at the time of switching wheels. (My suspension is no longer stock.) I switched at about 1,000 miles as mentioned, so this is a proper comparison of fresh vs fresh tires!
Stock for me was 20x9" Uberturbines wearing 235/35R20 Tesla-spec i.e. foam-lined Pirelli PZ4 280TW "max performance " category summer tires.
New setup is 18x8.5" forged Titan7 T-S5 ET35 wheels wearing 245/45R18 Bridgestone Potenza Sport 300TW "max performance" category tires. So same category, but different tire and no foam liner.
Better with the new setup: dry grip, wet grip, ride quality, wheel protection (from bad roads / potholes), tire cost, quieter when driving hard (the PZ4 were squealers, the Potenza Sport thankfully are not), power steering feel in quick back-and-forth turns.
Same/similar with the new setup, as best I could tell: hydroplaning resistance (didn't have issues with either tire), steering response (stock M3P mushy steering remained but didn't get worse than I could tell).
Worse with the new setup: Slightly louder on the highway (not a lot, I've had much louder performance tires and these are still very daily friendly to me, but they are a bit louder cruising on the highway than those very quiet OE foam-lined PZ4)