I came across a couple of resources recently that may shed some more light on the question of oil selection -- or perhaps simply throw gasoline on the fire! This link to the current Mobil 1 chart shows Zn and P levels for "SM" rated oils that roughly match the chart on LN Engineering's "Oil FAQ" page. Note also that Mobil 1 0w40 and 5w50 are claimed to carry more Zn and P than most other SM-rated Mobil 1 oils, but M1 15w50 is the Zn & P winner as far as Mobil 1 oils recommended for street-driven cars go. Check out M1 Racing 4T 10w40 -- it's SH rated.
http://www.mobil.com/USA-English/MotorOil/Files/Mobil_1_Product_Guide.pdf
The Lubrizol corporation - makers of various chemical products including components used in the manufacture of motor oils - has a really cool comparison tool. It allows the user to compare the performance of one (or more) oil specifications such as API "SM" vs ACEA A3/B4-04. That particular comparison is pretty illuminating, by the way! The king of the hill appears to be the Daimler MB299.51 specification, which is required in the Mercedes-Benz 3.0L V6 turbodiesel engine. Check it out:
http://sas-origin.onstreammedia.com/origin/lubrizol/EOACEA2009/RP/PC/index.html
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