Gutted for you mate - All part of the fun/pain though.
Look on the bright side if you went there thinking your car might be pushing close to 400bhp, and the car felt quick to you. With a new exhaust and possibly induction then your looking at a minimum of another 60 ponnies.!
Had similar problems with my classic 2.5 at the time, and first dyno the car pushed 340bhp/373ft/lb and I felt the car was a rocket at the time. In the end It was my induction not the exhaust that released the biggest gains, and 380/380
The revelotion 3" system gets great reviews and not too loud. If you running a panel filter in the standard airbox, you will also need to think about an apexi induction or larger IMO.
Its amazing how everything has to be balanced when you start pushing big BHP. One thing out of kilter and make a huge difference.