I'm looking to swap out the speakers in my doors and dash and have a few questions. First, I assume the stockers are all 4 ohm impedance, correct? Will I need to use spacers for the door speakers because of the bigger magnets? Will they still fit without touching the door panels? What size are the dash speakers? Anyone done this and if so what speakers did you use and how much of an improvement was it? I don't plan on changing out the head unit, adding a subwoofer or any amps. The stock system sounds OK, but I want a little more bass punch and crisper all-around sound. Thanks.