Here are 2 video clips. One is a litte 383 (prolly 500HP?) we built with a 3" Magnaflow X Pipe system, the other is the Back in Black car with a 450HP LS6 with a 2 1/2" Magnaflow X pipe system.
I have the Back and Black car in my garage right now for some magazine photos shots. I was driving it yesterday and commented on how nice and mellow (but deep) the sound at cruise was. I am a stereo nut and really like comfortable cars. I cannot stand stupid loud exhaust.
We run Maganflow on everything

Russ 67, 383 SBC / 500HP?, 3" Magnaflow X Pipe system, (650 and free shipping)

Back in Black, LS6, 450HP, 2 1/2" magnaflow X Pipe system ($500 delivered)