Yeah don't get the speakers they come with. Like I said, I have really good kickers with an amp powering them in the kick panels, and even with that the sound is pretty ordinary there, as there is no acoustic enclosure, and the sound is going towards your feet. So if you are going to have them, make sure the speakers are good. Good 6.5's aren't expensive either.
The rear package tray speakers will be the biggest changer, as barnett already mentioned.