I had several setups in my M3. First lowering springs, then Ground Control using stock dampers, then AST 5220 and finally AST 4200.
The AST suspensions transformed the car but the 5220 were problematic including several leaking dampers. I finally switched to the AST 4200s and used them for about 25 track days with the only issues being replacing faulty lower bearings on the rear dampers.
As far as the car was concerned it was a new car with the suspension and was easy to dial in, both the 5220 and 4200. The 4200 are, with a few clicks of the rebound setting, very comfortable on the street. On the 4200s I used 550 lb springs in front and 790 in the rear.
AW on Fox Red Extended, Alum trim, ZPP, ZTP, DCT, 19" wheels, Heated front seats, HD radio, Sat radio, I-pod & usb, Premium sound, AP racing BBK, 18 Volk Racing TE 37s, Akrapovic Evolution exhaust, AST suspension