My point exactly. How often have we seen a member swapping from high performance subwoofer X to Y and saying "well, that didn't work out and I think the one I had before was better", or even "meh, not much of a difference". Never would be my guess?
Properly calibrated in-room, outside of at their limits I wouldn't see much difference between most of these subs. E.g., with my dual DIY subs, they can pressurize the room a lot more than the PB13 did with content below 18hz. Above that it gets a bit more difficult to discern. Maybe shot gun blasts are better, but I'd have to go back to my notes as I don't recall a night a day difference even with duals during say the shot gun scene of Open Range for instance. My Pb13 was boomy too, until I used the correct calibration settings on the sub to tame the rising in-room response I was getting (I get a lot of room gain from 30hz down). After I spent hours calibrating the FR to be as close to the FR of my AV15H dual opposed subs from ~20hz up, they sounded more alike then not. Except what I seemed to recall being a distinct sonic signature of the Aluminum cones of the AV15H drivers, though even that I can't say for sure as this is going back a few years.
Heck, when I tried out my SB13 sub (that I still have, though it sits in a box in my basement at the moment until I move into a new house) I didn't notice much difference between that and my duals, except that it ran out of steam around -10 or so to db reference in my small-ish room.
After doing a blind test of numerous "high-end" subs in the same room at the same time (with a poor attempt of eq-ing them all the same, but an attempt none the less), I'm much less inclined to recommend anyone go from one high end sub to another given how difficult it was to discern differences even between ported and sealed subs for that matter. I'd focus first on the room and on getting the most out of what you have.
RobZ - can you post a room response? DRussell is asking the right questions, what is it you feel you're lacking?