Mine (similarly set up) was tested at Croft 2 weeks ago by the circuit and a static test at 4,500rpm gave a reading of 98.5db.
I was also tested a year ago by a mate - on drive by on the finishing straight at Croft going flat out at 102db.
I haven't had a problem at Oulton Park (tested static) but I can'ttell you what the reading is.
My exhaust can is showing some browning which probably means it could do with repacking (3 years old, 14K miles, 14 trackdays).