I seriously recommend a component setup with an x-over. This way you will get better bass and better highs. If you have the cash, Rockford Fanatics are good. The fanatic Ps are only around $200 and sound awesome. Alpine's R series are also good but will run you more $. Word of advice, junk your factory deck, burn it, stomp on it! There is no point in getting new speakers if you aren't getting a new deck. The deck simply puts out inferior quality sound and your new speakers will just play inferior sound. Ford's deck are made out of Sony's crappiest parts and suck. The first mod I made in my car was to tear that deck out.
The Honkeytonk
Monkey