If your not wanting to shake your doors loose then you can get away with a smaller woofer. I have seen amazing things come from a single Kicker Soloberic 8'. But Im not much of a stereo guy. I would consider F8L Z71 the for most expert in this area.

 

i have 2 8 inch solobarics in my truck now. they are runnin off of like 600 watts and sound pretty good, not to loud but loud enough. i used to have 3 of them in my 91. personally i would stick with 10's. after i had 15's and and 12's in my tahoe. i think i will stick with 10's in my truck. the 8's sound good but just can't seem to hit all of the notes i want them to.