I put 6.5s in the front of my P5. I don't think you'll have any depth issues - I don't even think the window gets in the way. There is a good amount of space in there.
I made some mounting plates out of 1/2" plywood, so they bolted up to the factory screw locations door and then the speakers screwed to the wood. This reduced the depth even further, so if you go this route you definitely won't have any problems.
The only issue I encountered was that there is a ring of plastic on the inside of the door panel - the stock speakers (at least in the P5) have a foam surround on the outside edge, and this ring pressed against it, creating sort of a tube from the speaker to the grille on the door panel. I had to cut this ring off (actually, I just cut slits in it and bent it back) because the plywood brought the new speakers too far out and the ring prevented the door panel from snapping back in place. Not a big deal, but I somehow bent the plastic grille on the door panel, and now it has that white, "bent plastic" look to it in one small area.
Actually, the speaker placement is so crappy, it almost doesn't make a difference. But I do they are marginally better than 5x7s, so whatever. Good luck.
