I have a pair of 12" kappa perfect's in custom 1.0 cu ft sealed boxes. They are as accurate as anything I've heard to date. And will get plenty low enough when needed. You can not go wrong with this type of application.
I too purchased a Silver speed. When I contacted Mazda for my production number, I was told by a gentleman named "Joe" that I was number 301 out of 1000 Silver's to be made. The dealer I purchased from had 6 speed's on the lot, 3 of which were titanium, 1 blue, 1 silver and a left over orange...