Subwoofers 10inch vs 8inch for fast metal?

i no alot of ppl use 12s but they cant keep up i want the hit of the 12 with the precision of a 6x9 cause **** i listen to like caliban lamb of god divine heresy fear factory has fast b/chug/blast beat double b parts and i no 12s usually cant keep up i was wondering does it matter square vs round? what kind of box is best ? what is best as far as ohms/watts via the speaker /amp i have a suburban with the 3rd seat out so i got room i was thinking of going 2 8's or 2 10's based on your answers with a box with 4 6x9s also plus a 6x9 in each rear door and 5x7 in each front door and tweeters i dont no **** about subs never owned em cause i thought they didnt make ones that hit hard / faste enough for musik thats 230bpm