That Rythmik 18" doesn't really have an extraordinary level of midbass headroom. The FV25HP is a different animal that does have a huge midbass output.
You don't think so? Maybe I just got my numbers mixed up from when I was looking at the FV25HP but I could have sworn there numbers were higher then the SVS 4000's even the ultra 16's in the midbass. By at least 25% if not more if I remember the numbers right when we went over them through the whole midrange.
But then again I'm comparing it to SVS who I feel specializes in emphasizing the deep waters especially with extended mode or more the 60 to 20 Hz range in standard and has good but not stellar midbass.
So maybe they measure good against SVS in midbass but not like you said the craziest out there.
Hmmm interesting I'll have to jump on data bass myself William! See ya over there!