lol stop arguing about power output. There are some nice torque curves in this link.

http://www.tomorrowstechnician.com/C...0000001985.pdf

I think for an RX-7 with an an original spec rear end and transmission the 4 port has a more appropriate torque curve for daily driving. Torque comes up faster and higher at low RPMs, offering increased fuel economy and better city driving performance over the 6 port. Plus it's cheaper to find one in decent shape with less wear and tear due to the lower rpm power peak.

Do the old 13B intake manifolds bolt on to the renesis?

No they will not. The ports are relocated but, I could be wrong.