Depends on your power, of course. If you had, say, 1000-1500rms, w6 would be your best bet, hands down. If you've got 2000-3000rms, type-x will be louder than the w6. Just the plain fact that the type-x can handle more power, but it's gonna be an inefficient beast.
I too was trying to compare jl speakers to the type-x, but i gave up. The type-x really isn't comparable to the w6 or the w7, it's a completely different speaker all over.
Performance wise, i'd put the x between the 6 and 7, but the strengths and weaknesses are too scattered between the 3 subs to compare them very well... Just my .02