Hi Hurmund,
I've just measured the speakers that came out of the front and they are 6".
I never bothered with the rear ones, mainly as I never drive in the back
Having said that I'm sure it would sound even better.
The sub easily fits in the footwell. I put big velcro in there and pushed it right up the back and it's fine. I don't think you'd hear it from the cubbyhole in the boot though.
cheers
Roger