I have a 2006 base model 300. I installed some Infinity Reference 6x9 3-ways in the front doors, and my window scraped them when I rolled the window down. It scratched up the window tint. I believe the mounting depth is around 3" for these particular speakers. I plan to put them back in the doors, but I plan to cut out a trim plate to bring the speakers out a little bit. But there definitely is a depth limitation on speakers in the front doors, just not sure exactly what it is.
INFINTY REF 6x9 Mounting Depth is 3-1/16
Alpine Type R 6x9 mounting depth is 2-15/16
so...i should be ok.....