I've ridden in H&R 'Cup Kit' setups on 3 series, and it was a little 'bumpy' as it was stiff, but the ride wasn't too harsh (till we hit speed bumps, OMG). Eibach's (Even a sportline kit) seems to give a smoother ride than a cup kit at least. Prokits, I can't tell the difference from OEM sports setup really (till you get to actually cornering).