IMO, the Gibson dual extreme system would be good. I installed one on my Ranger (3.0) a couple years ago. Idling, it is not loud at all, there is a small to moderate noise difference on acceleration. But when you really open it up, at speed and high rpms, it really howls.
While not noticeably louder than the stock exhaust, at idle and accelerating, even on my 3.0 I've noticed the exhaust tone/note to be much deeper. I can only imagine how it will sound on your 4.0. Also, it's very easy to install, hardest part(s) being cutting the rear section of the factory exhaust, and then getting the new exhaust lined up and even on both sides. Even to this day, I still fiddle around with the exhaust tips, adjusting them in and out, I guess due to OCD.
My vote; do it!