It's also how much power you send them. The numbers put out in TCAB boxes were run off something like 1500 watts RMS. They won't do near that well off 300 watts. In fact, I've been told they won't even start getting good until like 700. (Don't quote me on that). So if you're only running like 100 to 500 watts per sub and have subwoofer specific optimized enclosures, Shivas, DHM108Bs, and Beals 8s (//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif) are gonna walk all over Type Rs with their high efficiency.
My $0.02.