Surprisingly enough, they are very, very loud on lower frequencies... (I Put On for My City has a really low bass line that my W3's can pick up but that you can barely hear on my friends 12" Kicker Comp)... but I agree, the box is on the small side.
I would ideally like a single W6... but I just don't know if I can justify the price, and IME, JL's sound fantastic but they're kinda sensitive. My friend has two 12W6's and he's had a lot of issues with them... but I love the way they sound.
Theoretically, couldn't I just keep one of my W3's in there, but not hooked up to the amp, and have 1 10 on the other side?