My '18 M550i came with 19" Michelin Primacy 3 run flats. After picking up a sidewall staple in one I replaced the lot with Pirelli P-Zero run flats. The Pirelli's are, hands down, a better tire. I'm very happy with them and will likely buy a new set once these wear out.
The P-Zeros do have a lower loading index than the Primacy 3's (96Y vs 100Y in the rear, for example). One tire shop refused to even consider putting them on the car because of this. The dealership, on the other hand, was more than happy to do so. I personally calculated out the maximum loading and made a mental note to not drive around with four passengers AND a trunk full of lead.
I've found running a couple psi above the TPMS suggestions work best for the P-Zeros.