(~6K) RPMs at the ring/cylinder wall interface? Its detergent properties compromise the ability of the oil to lubricate.
Also, immediately upon beginning service the ZDDP starts to deplete.
How fast does it deplete? Well, from a test diesel engine (Mazda 4 cylinder inline OHV) producing 86.5bhp (at 3K RPM) and 22.9Kg.m (at 2K RPM) -- which I note suggest the test engine's RPMs are quite a bit lower than those experienced by our Porsche engines -- assuming 100% of the ZDDP was active at 0 km by 4000 km the percentage of active ZDDP was down to 23.6%. At 8000km it was down to 15.3%. by 13200km it was down to 2.0%.
There's more: As the ZDDP level goes down carboxylic acid goes up.
So you have to run lots of ZDDP to have any meaningful benefit (and its benefits are highly questionable -- I mean I have to point out most automakers recommend an oil with reasonable levels of ZDDP and the forums are not flooded with reports of engine failures or anything else that can be attributed to the amount of ZDDP in these oils) when the oil has some miles on, yet stay below 6K RPMs to avoid the risk of ring/cylinder wall damage and as the ZDDP depletes builds up acid in the oil.
More on that benefit thing…
There's the question of just how well ZDDP does what everyone believes it does. Spectromicroscopy of tribological films from engine oil additives one of the conclusions from looking at surfaces using x-ray microscopes found this:
The morphology of the alkyl and the aryl films are very different. The alkyl ZDDP decomposed rapidly to give protective pads of about 1–10 μm in diameter. In contrast, the much lower decomposition rate of the aryl ZDDP yields much slower, more uniform, formation of phosphate after a lot of wear has already occurred. There is no evidence of protective pad formation.
So run high levels of ZDDP as if it is some magical elixir.
But wonder what's happening at the rings/cylinder walls at high RPMs.
As the oil accumulates miles, work out how much of the that ZDDP remains to do its magic thing.
Think about those increasing levels of carboxylic acid.
Then recognize the stuff does not appear to form any protective anti-wear layer on the very surfaces it is supposed to protect.
What an additive.