96 T-bird 6 speaker setup

I just bought a 96 T-bird and was wondering if it would be worth the money to fill all six speaker locations with matching Infinity Kappa 5x7's, or only use two pair and leave the two holes in the rear deck open for the subs to "breath". I've never had this much potential to work with and don't know where to start.

Just finished a 90 Supercoupe with rear speakers (Focal 165V2). Xtant X2 12's firing towards the rear = a stupid amount of output and saweeet tonal response. I would put a good set of component speakers up front, then as I like rear fill a good set of brand matching coax speakers in the rear.