This thread is full of fail... (mixing speakers isn't good, frequency response will be different in a bad way.. you can get cancelling, which means some freqeuncies are much quiter)
Southnash, if u are a believer of QUALITY over QUANTITY, then why even bother using rear speakers?
I would only do speakers in the front, use good quality ones get a good amp to drive them, position and install them properly.(stock locations aren't the best places most of the time, and you need some deadening to make it sound decent and have enough midbass.)