If you do some google research you'll see some literature out there with numbers. I've read one study where it can reduce the noise dB's by almost 10 db. Pretty huge difference as it's a logrithmic scale. Don't think we can get that much out of an F150, but particularly if you've got some large tread on your truck, it'll make a big difference to go crazy with butyl.

SQ wise it makes a big difference in detail and avoiding resonance. So it's more than just exterior sound deadening, particularly if you have some mat and/or absorption material just behind your mid-bass. At volume the back reflections will impact the back of your cone, causing loss of detail, and if loud enough, audible distortion.

If you've overdone your subs for SPL, then it'll blow out your mids for SQ and it won't matter what you do to them.

SQAugs