The truth is that the so-called sensitivity advantage of the ported version is only seen in a computer model.
Every large ported sub is grossly under ported for the maximum output graphs that the models project.
Those 18s would probably need 3 times the port area they actually have to produce the modeled max output graph with no port compression.
The reality is that there is 2-4dB of compression at maximum output, and with huge non-linear distortions.
OTOH, the sealed system will show virtually no compression down low with much lower distortion.
The point is that what a model shows as a difference in maximum output at tune doesn't equate very well to the real world.
The max output from 10-20Hz will be basically the same, with much less distortion from the sealed system. The headroom above and below that will be 6-8dB. The transient response will be better by 2 octaves.
It's hard to predict anything from a subjective viewpoint without in-room measurements, but the systems, as a comparison on paper, are significantly different, across the board.
Should be fun in any case. Looking forward to impressions and details.