I've heard an S50 engined Z3M with baffles removed from the rear boxes (cut open and gutted).
Sounds simply awesome, very 'angry'.
I have a Supersprint on my 2.8 and I could hear that above mine when he was BEHIND me.
Gets me thinking that maybe you should look at the exhaust bypass valves, gives you best if both worlds (bypasses the back boxes completely at the push of a button then back to standard when you like).
There's a big thread on them hear somewhere, will dig it up.
Here it is:
https://zroadster.org/threads/exhaust-talk.8149/