1) None of that BS translates to anything you'll perceive in your vehicle with whatever enclosure you choose to go with. 2) The 500 series subs are built 100% in China.
3) There are no official, industry-wide statistics on reliability published anywhere....especially regarding origin of manufacture. The outcome would likely be unnerving.
4) In a show 12+ years ago in NY state, I assisted a competitor in a ZX3 with two Rockford entry level 15s in .75 cube sealed truck boxes do a 148 on the dash with an MTX 2160 amp. SPL numbers mean jack and have no correlation to audible performance, especially when comparing one vehicle type to another.
5) Ask DD for the "Le" parameter on the 500s. The inductance is substantially low on the E15. This translates to good transient response or lack of muddiness.
6) The real performance will come down to your enclosure design. If you waste your time playing with someone who plays with WinISD or BBpro, you'll be tinkling upwind.