I would have to side with jinjuku. I have 600 watts going to my Kappa 12VQ from a Peavey pro-audio amp and that sub is clean as can be, even when I'm cranking it.
I would still be interested in a side by side of a large 18" driver sealed vs. a highly capable 12" vented design.
My speculation would be that you would need considerably more power going into the 18" to add EQ to the low end so that it rivals the output of the Kappa midQ design below <30 Hz. Above 30 Hz...I've read good things about the smooth upper bass the maelstrom has but have never listened to one. The Kappa VQ has an effortless, smooth sound all around so it would definitley be a toss up.