It's no secret that the plus series is the value leader. Comparing the two drivers, is the ultra basically more headroom, resistance to bottoming, impact, and max spls? Or is the bass better qualitatively as well? If the PB2+ can do 115db or more at 25hz as others have reported, I don't need the extra power the ultra driver may offer. I'm more interested if the bass sounds "better" at reasonable to loud volumes.