Another useful post by RangerDanger, what a surprise.
Regardless, the W3V3s need some juice to really make them shine. If the box totals a 2 ohm load, they're seeing 300w each. If its at 4 ohm, they're seeing 200w. Somewhere closer to 1kw would be optimal.
Nonetheless, every car is different. I've compared a couple JL 12s in my Mazda 3 trunk, then a 02 Jetta and a 06 IS350 (i placed my box into their trunks, and ran a wire through a window to my car's amplifier). My car didn't get NEARLY as loud as the WV nor the Lexus. So the car itself can make a big difference.