I used to run a pair of 12s in my explorer... it already had the factory upgraded sound system or whatever because it was an eddie bauer. I used to be a fan of big bass sound, but here recently my friend has been showing me all about *good* audio... crystal clear sound that is as clear and balanced at low decibels as at high. His setup is mind blowing...

But here's something to think about... it takes 12 feet for a bass wave to mature. Meaning it forms, peaks, and dies in 12 feet. If you have 12 feet of interior space (or more), then you will have less feedback issues. Since you mentioned driving an escape, I don't think you have 12 feet of space, which means if you put subs in the back, they will be coming up, hitting the dash/front of the car, and then reverbing back into themselves, which is gonna give you warped sound/reverb problems. The way to combat that is to keep your sub size smaller. The deeper the bass, the longer the soundwave it creates. I would stick to 8s or 10s. Also, you said you listen to a lot of metal and rock. Those are both musical styles, as you know, that don't rely on bass (like hip hop and techno), which means you should concentrate on upgrading your whole system, not just the subs.