The low Q on the 5200 does 2 main things. One it makes it one heck of an SPL sub if you get the right parts on it, it will peak VERY hard right near tuning, that also makes it very hard to design a good box for one if flat response is your goal, at least ported. Ported it will dig low, in a fairly small box, minus the huge port in needs of course, airspace however can be pretty small. Also, nice thing about the .15 Q is that if you seal it, you can literally make the box as small as you want, as the Q will never be over .5 IIRC lol. You basically get the same output putting the sub in a 2 cube box as you will a 5 cubic foot box.
Best way I can put it, it's not always about making the best sub.. It's about making the best sub for your application. Without knowing what kind of car this thing is going in, how big a box you want and how you want it to sound, it's basically all pissing upwind. For example, if you wanted output above 60h, because your midbass only make it to 80 with authority, you'd be unable to do that very easy with a 5200. Only way I can think of would be a 6th order and again you'd be fighting the woofer, especially if you went with the 8 layer coil.. See where this is going? It all comes down to what you want. And if you don't know that, it's best to honestly, get an off the shelf woofer until you figure it out.. All, IMHO, but I've been around a while and seen quite a bit. Most people jump from supersub to supersub for this very reason, they A. don't know what they actually want from a sub and B. they don't know how to get it.