My speakers were blown so I got four 4" Pioneer cheap speakers from shady wholesale dealers in downtown LA. They work well enough but you can tell the sound is lacking. I've got the pioneers up front and in the hatch but the two 3.5" open air speakers in the rear seats are still there. I couldn't find a good replacement for those since they were not enclosed.
basically, 4" sounds good enough but it is not great, in fact, maybe its not good.