Okay buddy, if you can't tell the difference in 139 and 144, something is wrong. Get your ears checked. That's a SIGNIFICANT difference. And I don't see you hitting 144 with W3's unless you're talking about a multiple 15's or 18's. Sorry.
sx's are mostly spl with a lil bit of sq, while q's were made with sound quality in mind first, they have the ability to get pretty loud though, lol. I'd go with the Q after owning 18's of both...Maybe try a RL-P, Type R, CVX, DC LV4, DD2512, etc.
Okay, most people realized that the XXX was a great sub like 5 years ago? And you could afford to give it about 500 more watts too. I had an 18" version. Loved it.