I had a set of 3" B&B's on my 92'vert . They were an early system and I had lots of resonance at cruise speeds around 55-60. Once I got to 70, the resonance went away. The worst RPM range for the resonance was about 1200-1500 RPM. The one thing that did help was running in 3rd (it was an A4 car) at speeds under 50 in town.
What was interesting was that with the factory hardtop on, the resonance went away. :confused
Other than that, the sound was great and definitely a deeper sound than other systems. Expect about a 10HP gain and 15-18 ft-lbs more torque.
B&B makes a 2 3/4" system with a re-designed resonator that is supposed to pretty much eliminate the resonance. If you don't have a specific need for the 3" diameter pipe, I would recommend the smaller pipe. B&B also has an X-pipe that you can substitute for the resonator when you order the system. If you want it later, it's about $300 :eek
Installing my system required me to cut one of the rear pipes, but it was one of the early systems. The metal is very thick and everything is polished!!