I'm gonna stick with 10" or better. Sealed box(tighter bass, but not quite as loud as a ported box) make sure you have a good amp, and good mids and highs witha good amp for those as well, or youll just have a lot of bass, and no treble, which would ruin dubstep. This is my setup and I think it works very well.
rears: 2 Kicker 2 way Co-axial's, and 2 6.5" Kicker components in the rear deck
fronts: 4 Focal 4" 3 way co-axial's.
sub: Memphis M310 10" sub in Memphis ported box
Amps: Alpine MRP-F300 for the mids and highs and a Kicker ZX400.1 for the sub.
Head unit: Pontus 7" double DIN touch screen
sounds great, and can get super loud if I want it to.