Kraft made some good points...and in the end Steve, Music has always been about personal taste. It's really about what sounds good to you and where you want to take your system. I personally think it still all comes down to volume, acoustics and Sound Quality. A quality 400/800 watt 10" speaker is the way I'm leaning.
I found this cruising the net...
"The acoustics of your vehicle also influence bass response. The small interior size of most cars and trucks boosts low frequencies dramatically. You will need to use a smaller enclosure then normal to achieve a flat bass response. As a rule, below 50Hz (depending on cabin size), bass response increases at about 12dB per octave as the frequency decreases. This "Cabin Gain" adds significant bass output to the subwoofer system."