To put into perspective the range of rebound there are 18 total clicks. You shouldn't set it on all the way hard or all the way soft. So essentially 6 clicks=1/3 and 9 clicks=1/2 of the range. Depending on what you want to do with your car and it seems that you prefer a more comfortable ride, you may be happier with sleeve over system. There's a couple good reviews out there. For everyone else, there's plenty of other threads with arguments about OEM suspension vs. KW vs other brands. The OP is asking about KW V3 compared to the stock ride qualitiy.
'09 E90 M3 SG | VF620 SC | BPM Sport coding | AA Catless Exhaust | KW V3 | BMW Performance Wheel | Alpine 8K Eyes | 355M Style Wheels | Recaro Child Seat
'13 X3 DSB with M Sport | H&R Springs | Gloss black grill | Coded by me