Well I just sold my 03' V8 Mountaineer (4.6 V8). I had a Mac Intake, headers, and a true dual exhaust with a custom x-pipe. I used two CGS mufflers. Truck sounded badass, ton's better then a similar setup I heard with Flowmaster 40's. It sounded more like a Cobra. Not obnoxiously loud like you hear on a lot of pickups, just a deep, very aggressive sound. And what a burble at idle, Ford's modular motors have that watery burble down low and at idle that I love.
I still have my 00' 5.0 Mountaineer for now, and it's stock. I'm getting bored of not hearing that ripping V8 sound lol. Ordering a Mac Intake and having another custom dual exhaust made, though this time just using a dual inlet/outlet CGS muffler.
I can tell you this, with the mods on my 03', I could pull high 14's in the 1/4 at Moroso, pretty damn quick for a regular suv with just those bolt ons. Fords 5 speed auto keeps the engine in the power band constantly with 3.73 gears, and Ford really bottlenecks their trucks/suv's in terms of intake/exhaust flow. Plus I use to get 16 mpg in the city with a lead foot, and 22-23 mpg highway at 80-85.
What I hate is when you hear trucks/suv's with what are obviously glasspacks, ugghhh, that's one way to ruin the sound of a V8. Even when we still had our 502 Chevelle, we kept a full exhaust on as the sound of straight pipes or glasspacks even on a muscle car IMO make the engine sound all hollowy/raspy. But I guess some people like it raspy so.....