All I can tell you is that when I blasted some drum'n'bass music and A/B'd the Rythmik vs Outlaw, the Outlaw could hit harder. This is not guessing or pulled out of thing air, this is just what I experienced when I ran both subs as hard as I could push them. Keep in mind this is music that has its fundamental around 50 Hz or so. The Outlaw simply had more headroom in that frequency range, but that is only anecdotal evidence and shouldn't be taken too seriously. That it can get louder is not surprising since it has a larger cabinet, a larger driver motor, a bit more amp power, and larger port volume, but of course it is more expensive; we are comparing a what was then $500 sub vs a $750 sub, and it is not a fair comparison, but it was what I had on hand. I didn't have the measurement equipment or understanding of these things that I do now.
I doubt there will ever be any meaningful data because Rythmik hasn't sent a review unit to any reviewer who does measurements since the FV15HP, and that was years ago. I would love to take a Rythmik sub out to measure someday, but I don't think that will ever happen. I will say that the FV12 could retain its composure better at the edge of its performance envelope than the Outlaw. If you push the Outlaw hard enough with deep frequency content, it will obscure detail, but that didn't happen with the Rythmik. Then again, I didn't push the Rythmik extremely hard with deep content, because it wasn't my subwoofer and I didn't want to risk damaging it. It was a very good sub and a steal for $500.