As one who has a set of staggered 18-in AMG lo-pro on a sport chassis: they can be a bit hard on the bum. Pirelli are smoothest ride but I ditched them off the front for vague wandering in the wet, Michelin having better grip. Do watch they clear your wheel arches if you have lowered sus: for example 245/40 do not clear S210 sports front even with the factory modified arches, 235/40 do (265/35 rear). Get the offset right too, the 18s need offset studs.
If your sus is higher and softer then the big 18s may work better, I would go with slightly more sidewall but I'm stuck with the wheels.