I have yet to find an 18" that models better for MBM duty than a BEYMA 18P80ND:
Having uber-high sensitivity, power handling, and a fair amount of cone area is the key to loud mid-bass.
Also, having the impedance peak within the passband helps keep the coils cooler and amplifier less strained.
(xmax/xmech and horned box would help too, of course.)
That said, it is 5x more expensive than a 460. But yet only about 2-4db louder...
I'm building this:
16 Dual-Opposed 460's sealed
Which gives me this with 8kW:
(Note: I don't have space for ported, and I don't have space for 21's.)
With 16 coils it will basically never heat up, and it only costs me $1600 in drivers.
16 Beyma's are 2-4db louder in this config, but it would cost as much as a new Tesla M3.
Porting the 16 460's gives you this:
Which isn't much of an improvement considering these boxes are the size of bathroom's...
It does however require only 3kW at this point, but also HPF's too, of course...
122db @ 20hz is not insignificant.