Speaking from my own experience, the front dash and rear speakers on a 300CE are 120 mm. IQ car audio has them but you'll spend >$300 replacing all four. i found some, "Carpower" by Monarch, a German mfg., from a European supplier. A set of four cost me $100, shipped. They are direct drop in for the dash, because of some spring clips attached to the speaker frame. Not sure if the door speakers are built the same.

I don't know how these sound, as I bought and installed the IQ speakers. I still have them new in the box if you're interested. Impedence is 4 ohm.

There is a thread in this forum with pictures of Carpower speakers being installed in a 300TE. Shouldn't be too hard to find.