LOL
Why do you wanna get to 150db!? its not as big an achievement as it used to be, the big boys are hitting 170+
If you aim for a volume you may be dissapointed, build it up for the sound you want, with that much cone area and power it will be plenty loud enough.
I shall have to dig out some pics of the wall i built with 2 * RE XXX 18's with 2k each from SPL Dynamics amps - used to make my eyeballs vibrate when it hit a low tone! The poor old Rover 416 didnt know what hit it.