Here is my 07' 335i with DP's, and secondaries swapped out for vibrant resonators....stock mufflers. I actually really like it....it's quite when cruising around or on the highway, but sounds sounding my better once you get the RPM's up.
Flows good enough to let the car run 10's in the 1/4....so it's not like it's holding it back much. I have the burbles set to "light".....
Oh, and it's not smoking...it was 35 degrees out last night....so you are going to see some steam coming out of the hot exhaust.