The door cut-outs are oversized and you'll need mounting plates for new speakers (often included). You can easily fit 6.5" or 6.75" in the front doors and 6.5" in the rear doors. The front speakers do not fit in the rear doors without trimming because the stock speakers require an oversized cut-out.
they are stamped "pioneer" on the back but they are pretty much OEM in terms of quality. The front speaker actually have rubber surrounds but the cones are plastic. The rear speakers are have paper cones - a very typical OEM standard. I literally tossed the stock speakers in the trash when I replaced them. I think what makes the stock speakers sound OK is the SSP. With aftermarket speakers all the digital sound processing so carefully calibrated for the stock speakers goes out the window. It just sounds waaaaay too processed. That's a good thing because better speakers sound better with little to no manipultion to the EQ.
I've been waiting to replace the sound system in my car until I can get a radio adaptor to my aftermarket headunit. I have all the other stuff that I need and work with the first Certified Master Installer in the US and he has offered to help me out with whatever I need to do. So until then I'm just buying my time.