I have spent a good amount of seat time in a Z4MC. (Toronto to Spartanburg & back)
OE car except the SS race cans.
The exhaust can definitely be heard in cabin
, but I didn't find it objectionable at all.
I had the powerloops on my previous M roady & found them OK but wished they were a little more aggressive.
I'll be going with either the SS race/sport or RE Diablo this time.