Since you mention publications in OZ I came across an article on this Australian Jaguar Drivers club site. It's by far the most common sense assessment of the ZDDP issue I've read.
http://www.jaguarhunter.org.au/Technical_Pages/Modern_Engine_Oils.htmThe key points for me were:-
Not all oil specification place limits on ZDDP
It's not as simple as comparing the declared % ZDDP content as the restrictions have driven new more effective formulations of ZDDP.
Too much ZDDP is as bad or worse than too little. The whole issue is so complex that unless you are a oil professional it's got to be better to buy quality oil than add ZDDP as an after market additive.
The ACEA specifications have tougher valve train wear tests than API
ZDDP protection doesn't even work unless the oil gets hot on a regular basis. This is a real issue for me in the winter and I'm going to have to think of some way of limiting cooling. Look out for pictures with my engine wearing ear muffs !