canadapettit: Thanks for the info. Sounds like you have some experience with the pioneer and other subs on the market. Can you compare it to a JL 12W0 in terms of extension and SPL? If the extension is about the same and its just the SPL that suffers, I can probably live with it.
scott_fx: Thanks for the recommendations. Unfortunately, the 3 ID lines of subs are all 5.75" mounting depth at a minimum. ID makes great stuff, but the extra 2.5" of mounting depth (compared to the pioneer) is going to be a deal-killer. The problem is that it would cramp the fit of my golf clubs in the trunk. Since that's my job, the clubs take priority.
I took a look at the ed midbasses and they seem like good drivers. I would guess they're pretty similar to the JL 6W0. Unfortunately, I couldn't find Thiele-Small parameters for the ed drivers to compare to the 6W0. It would have to blow away the 6W0 for me to replace a 6" driver with another 6".