I have found thermal limit on these subs to be around 3600W, set with a 0dB tone. Any more power than that and the motors start heating up pretty quick. It's a bit of a bummer, because they have a lot of throw left. I may also be doing something wrong, but I don't think so. Nevertheless, I'll be doing more tweaking and testing over the coming weeks. These subs are mainly built to sound great at decent levels, so I can't say I'm super disappointed. Once my Levi gets back I will be much more focused on tuning the front stage, and the system as a whole, so I won't as be worried about getting the subs as loud as possible. I'll be focused on my original goal, dat SQL.
The good news is, the problem I was having with the PRs bottoming out will no longer be a problem, at least definitely at this tuning (I'm at 30Hz right now). I'll be playing more with tuning, now that I know where I have to leave power. It is a balance, though I'm positive I can tune down and still be alright. How much weight exactly I can add before it overcomes the suspension, well that's something I will find out.
If I do get bored with this, plan is to sell these subs, buy a pair of Tantric HDDs, and build a regular ported box. But that's not gonna happen for another couple months.
Oh, and my door panels are being sent off to @04murdalanche ; as soon as I get a shipping label for a proper fiberglass treatment