Ed, i've tried the following on mine, in this order.
Magnex oval - Nice sound, not intrusive at all, especially when cruising.
Scorpion - Compared to the Magnex, it was silent. Didn't like it.
TSL Firestorm - Bit louder than the Magnex, slightly more aggresive noise, especially at higher revs.
HKS Hyper - Loved this one, fair bit louder than the Firestorm i found, but i wanted more noise.
Blitz Nur Spec R - Fantastic noise, nice'n loud, but started to do more long distances, and decided to change.
Hayward & Scott - Noise levels probably the same as the Magnex, although the Anti-lag kinda killed it a bit.
The blitz and H&S were only ever on the car with HKS headers, so not sure what the rumble was like i'm afraid.
Sorry to go on, hope this helps.