Gents - Even Noussaine's chart is of mostly out of production subwoofers. As a general rule, at least here in the Colonies, most of the high output subwoofers use multiple 12 inch drivers in either a horn loaded (see the b-deap from servodrive.com) or ported (see the B4+ from SVS) ... Even the 18 inch based subwoofers take a back seat to those designs.
The B4+ is rated at 122 dB/16 Hz/1 meter @ 10% THD ... That is powerful.
I looked into importing a servodrive sub...... the bdeap is great in a serious custom cinema, but you need custom enclosures for them which really rules them out for most.... the conta is, as you say, a more conventional sub in every way other than performance
Unfortunately Mark took about a month to come back on shipping so I had spent the money already!