Great thread, only thing I can add is that for 911's the Bosch of choice would be silver, not platinum. (At least for my SC). Platinums are a lot cheaper, NOT top of the line. Also on my BMW, ('84 533i), I used platinums at first, did not run at it's peak, switched to the correct Bosch silver tips, now it screams and barks.
NGKs are very popular w/ Porsche mechanics I've met, have not tried them yet in the 911 but would not hesitate to. Apparently the cars really like these plugs for some reason, (run great).
