Joe,
Check out these articles relating to Rotella, which is a CJ-4/SM rated oil and uses a reduced ash formulation with less anti wear additives (mainly Zinc and Phosphorous) and see how other Porsche owners have fared using this oil.
http://forums.pelicanparts.com/porsche-911-technical-forum/367300-ultimate-motor-oil-thread-why-we-hate-cj4-sm-oils.html
http://forums.pelicanparts.com/porsche-911-technical-forum/332678-new-shell-rotella-15w-40-now-has-boron.html