For your front doors, the stock size speakers are 6x4 which is poop. Using custom mounts you can fit 6.5"'s in there.
I'm running a set of JBL GTO 607c 6.5" components in mine. Took the stock plastic speaker mount to a local car audio place and for a tenner the guy made me a pair of MDF mounts which did the job. Sounds so much better now.
Got a set of 6.5" Pioneer 2-way ts-g1702i on the rear shelf. 6.5" is a straight fit on the rear shelf.
Just FYI the front speaker mounts also form part of the front of the door pockets. If you make replacements you may want to bear this in mind. The stock mounts can be modded (I did) though I suspect that MDF mounts would be a better option if done properly.
Also note that the rear speakers run off a little amp in the boot. You will most likely want to ditch the amp so will need to do some rewiring there.