here is a good test done by grassroots motorsports. It doesn't necessarily go by "sound" but you can read a lot about competing exhaust systems. It does give info on the dB level of each though...
991.1 C2S PDK, Guards Red | PDCC | Sport Chrono + | Clear Tail Lights | Alcantara Steering Wheel | AWE Switchpath Exhaust
Previous: Porsche 997 Turbo 6MT, Atlas Gray | Cobb Stage 2 | HRE FF01 | Europipe Stg. 2 Exhaust | GMG LMS Rollbar | GT2 Exhaust Tips | Pagid RS-29 | Rennline Pedals | SSK
997.2 Track Car, heavily modded & E92 M3 DCT, still miss her daily & E92 335i heavily modded