I had two different sets of tyres on the 19s on mine, neither were run flats (l fitted a set of MO Continentals) but the 30/35 profile and steel spring setup up front meant that on anything other than smooth roads it was a very harsh ride. I found the seats uncomfortable on long journeys too.
Okay when pressing on, but not ideal on typical speed hump/potholed/general UK roads.
The 18s did make a marked improvement, although I had MO Dunlop Winters on those wheels.
It’s an E-class, so ride comfort should be reasonable even in an AMG IMHO