I installed some ST coils on my E92 over the weekend. Rides 95% like stock sports suspension. Very smooth and soaks up bumps very similar to stock. The only place I see any difference is on the highway over expansion joints going 30-40. Car gets a little bouncy. SLower or faster and it rides like stock.
Other difference is MUCH less body roll.
Great upgrade. You wont be unhappy with a set of STs.