That little sub digs deep in the right enclosure. Perhaps I missed it, but how many of these subs are you planning on running? You're drastically losing cone area if you only use 2. 4 of them, and you are really close(still slightly under) the cone area you had with the TypeR setup. What you need is a proper box for your vehicle, and possibly to experiment with different box setups. BassBarbie on.this site put up some straight retarded numbers for a couple of SA8s. You may check get build out, she did BUNCHES of testing though and put the time in.
OP, you sound smart, do your research, buy your equipment and BUILD. Honestly, at the end of the day, you're looking at a Sundown product, it will be well designed and constructed. I can't imagine you being disappointed, unless a mistake is made in your install. Im a big fan that it is HEAVILY reliant on your enclosure, the results you'll get.