I'm using the -30 / -30 KW suspension and I've to say I'm surprised in a positive way.
I'm driving a sport version so I only know the difference between the sport suspension and the KW suspension.
I've to say it's harder, but when you're driving normally in the city it's still very comfortable. The way you're driving faster it's getting harder, but you won't feel every grain of sand on the road ;-)