Here's the thing..."loudness" comes from your sub(s) anyways. There's no way a set of components alone could ever hit what a decent sub does...so thinking that adding 2 sets of components is going to make you "louder" than 1 isn't necessarily true. Again, the reason I say it's overkill is because 1. it can create an unbalanced sound stage and 2. if you are serious about being "loud" then you're going to have a decent sub/amp combo to begin with...which in turn is going to drown out the rear fill anyways. Even so, like I said in a previous post, if you invest what you would have spent on 2 mid-end components instead on just one more higher-end component and a decent amp...it's not only going to sound better (quality AND imaging wise), it's also going to be louder.

But it is your car, your money....do whatever makes you happy.