The XCON speakers are designed for Daily listening, not SPL Competition. You said you already had a ZX 1500, They usually put out around 1700-1800 anyways if I remember right, an XCON 12 would make up for the slight difference in Cone area by being able to use all of the ZX1500's power instead of having to turn it down to accommodate for the W7's weaker power handling.
I will be running a ZCON 18 in my daily driver.
Box design is key when it comes to how a speaker sounds.
There are many more speakers that will take all of the power from the ZX much more easily than a W7.
Q12 - Fi Car Audio Store