8's are very popular on this forum, look at the digital design 1508, the audioque sd28 (audioque is a sister company to digital design (dd) and the sd28 is supposed to be very similiar to the older dd 1008 (which was replaced by the 1508).
It's very easy to get a loud setup with only a few 8's
I have 2 dd 1508's on a alpine mrd 1000 in a 1.5 cuft box tuned to 38hz. There not bad for 8s, they get surprisingly low. Alot of peole are shocked when they see it just 2 8s doing that. Im about to get a new deck soon so hopefully itll be louder and sound better than my stock dash. anyways heres a link to vid.