It depends on what you mean by 'better!'
As usual, we are not told any useful details -do you have an M52 tu engine? In this case the RH exhaust outlet has a flap valve which is normally closed to reduce exhaust noise, which opens at about 3500 to 4000 rpm. Exhaust noise therefore increases from this point.
The usual exhaust note is a bit of a drone, and things are not much different above this point - but why people want more noise I cannot imagine - except to hopefully make an impression on bystanders.
The only really nice sounding Z3 models are the 2.2 and 3 litre types, which use seperate pipes and front silencers for each 3 cylinder group. These sound like a reaL 'six' in the way that an old Jaguar XK 150 did.
If you want noise, have the front silencers removed, or buy an after-market rear silencer such as Eisenmann, which is lovely in small doses and when passing through a tunnel, but is a real pain on long runs. I used to wear earplugs, and eventually had a custom-made exhaust system built, which is ultra-quiet, like a 328 saloon. As someone once remarked, noisy exhausts are for the deaf or the immature . . .