Actually, I would get 6x9's for the front doors. They fit in just fine. The only thing you have to do is drill new holes for the screws. This opens up many more possibilities. You can even fit 6x9's in the rear doors too, but this involves cutting away a little bit of material from the doors.
By the way, I have 6x9 infinity kappas in the front and 5x7 kappas in the rear. They sound really good. I do have a 12" sub in the back too, but even with it turned off, the door speakers sound good. Hope this helps. Let us know what you decide on.
