FYI, i mesured the box, well i had another identical one, its slanted at an angle, so the deeper part to the outter edge is 7 inches, the point the most shallow is 5.5, so were looking at 6.5 in the center..

 

Geared towards SQ .......
Infinity Kappa Perfect VQ
Alpine Type R ....should give u SPL and decent SQ
Resonant Engineering SE is a known to be a decent SQ woofer
Image Dynamics IDQ
Acoustic Elegance AV12
JL woofers are known to be SQ...but overpriced though

Google these and check the required measurements!
And ofcourse i advice going for a sealed box for SQ until and unless you can custom build the absolutely perfect ported box for your driver.

Btw SPL = Sound Pressure Level ,,,,yes it means loud

 

ic,, yaa the box i have is sealed,, and i prefer sealed over ported,, so i will check those subs out,, thanks for the info