I'm thinking, if you don't care about the trunkspace, get rid of the 10s, all of them, and get a really good 15" driver and mount it in a tuned ported box. With it's cone area alone it would kick the tens asses for SPL, and that's talking one 15 vs. two 10s (althouh a really nice 15 will more than likely get as loud as everything you plan on tossing in your trunk) A single 15 will also be easier to get sounding really good since you aren't mixing different equipment with different abilities.
The more different equipment you start tossing in there the harder it will be to make it sound good. Loud is great, but noisy gets old real fast. So says the guy that once had 14 speakers in his Contour, and has since gone down to 7 (custom 3 way front components, and a 15" sub) The scary part is that by choosing better equipment, less drivers are more capable than the wagonload I had.
