my stereo sounds awesome...I'm not sure what size the back speakers are but the 4 fronts are:

2 4" in the bottom of the dash
2 5.25" in doors
the back speakers I think are 6.5"

I know my 2 4" speakers in the dash were replaced in japan with some aftermarket ones, not the greatest but sounds decent.

I am pleased with the way it sounds though. I put a Phoenix Gold 12" sub in it.