Late response here, but I've had a pair of Seismic 110's for years. They're good subs for the size. I've never measured below 20 Hz or to the limit of the subs, but in my living room 2-channel setup I have no issues down to 20Hz. At the volumes I listen to, which can get very loud with music, the subs have never showed signs of distress.
Between the measurements I've seen on the e-Sub 110, 112 and Seismic 110, I think the Seismic would fall in between the 2 JL's in terms of performance.
Honestly, I doubt Paradigm is making a sub/driver like this:
IMO the Seismic 110 and E-Sub 110, while dissimilar, are still probably the most similar drivers on the market to each other. Paradigm's magnet stack is in the middle of the motor assembly (in between the 2 spiders), but they both have deep motors with spiders spaced several inches apart which is unique to those 2 drivers as far as I know. When the E-Sub came out my first thought was that JL took some inspiration from Paradigm's driver design.
Paradigm shaped the Seismic's aluminum cabinet so the driver would take up the whole face and JL just made the driver mounting flange the size of the entire front baffle.