have a freind who is wanting me to install some speakers in his daughters z28. Ill have to buy everything so i want to make sureiknow my sizes first. as of now it has all stock radio and speakers, so its unmolested. crutchfield says 4x6 in the dash and 6x9 in the rear seat location. are these the best sizes?

what about door speakers, i dont think hers has any but would doing the doors be better than the dash speakers? if so, id assume maybe a 6.5"....any help is appreciated!