Holy cow! folks running a lot of large speakers.. Not my thing. I have my 1-8" polk running of a 250 Kicker amp. It doesn't take up my whole trunk, has all the hit I need, actually more than I need, I have my amp half-mast to keep from overkill. A single small speaker can really do a number, if boxed correctly to factory specifications. Mine was the single 8" in a box, made by Polk Audio.
I am just one of those fellas who value quality over quantity. My car stereo isn't for showing off, but for sound purity. The extra volume is just a plus.