jl audio 10w7 or 12w7?

I'm looking to add some bump to my 97 BMW M3, from my research I've narrowed down my choice in equipment to JL Audio, I'm looking at the 500/1 amp to power the sub and just can't decide between the 10W7 or 12W7 in a sealed box. I've got the new Alpine 9887 as my HU and the rest is basically stock, rear speakers were upgraded with MB Quart's.

It is simply a matter of how much space you are willing to give up for a box. Both of these subs have a nearly identical group delay (response time) and the band width only varies by 3 Hz. The 12 will simply play louder. Even with the same power.

In the event that you have 3 cubic feet that you can dedicate to the box I strongly suggest a properly designed vented enclosure. I have built countless enclosures for both of these subs. In a sealed enclosure the group delay (response time) of these subs is very poor at high volume levels. This is a consequence of the high excursion/overhung design. Vented enclosures when properly set up do not suffer from this nearly as much.
You should also know that the “Q” and “infrasonic” adjustments on the 500/1 are built into that amp specifically for vented enclosure design. The amp is made for it.

Hmmm, interesting. So a vented enclosure is the way to go then, will I still get good SQ? I'm not ALL about the SPL, I'd like it to be tight and accurate as well as pretty loud.  Thanks

A properly designed vented enclosure in this case will yield you lower distortion, faster response time, and more output with less cone movement. To me that is what SQ is. To others SQ means that they are psychologically more comfortable with an inferior design so some people will disagree. Personally I love the experience of effortless and responsive sounding bass and that takes a sub that can play at loud volumes and at low frequencies on demand. Basically if you engineer the machine to perform equally under extreme conditions the non SPL tasks will be a walk in the park. The key is to not compromise SQ in the design, which is easy to do since that’s how JL designed these subs.