Well I was thinking that if I was building a cabinet then it would be 3" narrower using 12" drivers compared to 15" drivers. I'm not quite fussed on height as long as it's <1.5m, but I guess that only 3" wider for almost half the height (bc half the # of drivers) is probably pretty good too.I can use a router to cut everything from straight to curved. Just take your time and dont go deeper than needed each pass. I like the JBL's but not a big fan of the infinity. I think to do a 8 driver 1260 cabinet would be very large for the size drivers you have.
For the money I would do a quad JBL GTO subwoofer.