928fan4life

I just finished installing door speakers into my 1980 928 and now I am going to be doing the rear speakers. Since I recovered the back quarter panels in new leather I want to surface mount a set of rear speakers. Where is the best place to install them? Should I put them in the original spot in the a-pillar or should I put them towards the back? Also,what is the biggest size speaker that will fit in the original location where the old speakers were in the A-pillar? I believe the factory ones were 4 inch, would a set of 5 1/4 inch ones work? there doesn't seem to be alot of room there for something bigger,maybe a set of 5X7? Any input would be helpful