Just a further thought or two.
I'm running 17" wheels. I bought a second wheel set and fitted non run-flats to them, (Goodyear F1 GS-D3) before fitting the FSDs, and found the car was improved for secondary ride. But it showed up the standard damping as too soft over sections of road where a good damper will absorb the shock in a single thump, the OEM damper (even at 9k miles use) would be like a "one and a half" type thump out. The FSD sorted this, but trying the RFT wheel set, I had major improvements, but the RFTs were still giving issues to steering, grip, etc., so back to the non run-flat wheel set. I've since replaced the Goodyear with a Falken 452, (great results here in the UK with Falken on the 3-series) and the car is even better in road feel. The Falken in 17" sizing, along with the Koni FSD seems to have hit the spot, as it were, suspension harmonics are much improved and makes the car feel much more mature in driving feel. So much so, trying other BMW models (looking to replace the E91), I'm even more disappointed with the current suspension dynamics.