Went for the BCS Powervalve one in the end - quiet when you need it to be (i.e. normal driving - city or motorway), plant your right foot down and the valve opens up and makes a wonderful noise. Not boy-racer-ish but sounds just right (burbles and pops). It has the power to go with it, so it doesn't sound daft either.
I am now running at Stage 2 R-Tech remap, pushing 273bhp and 344 lb/ft torque. Most of the power is in the midrange, where it's actually required most.
Like I said, let me know next time you're up in Notts and I'll take you for a (sophisticated) blast.......