The chip's "Performance Controller" (i.e., CPU scheduler) will need to be Perf Tested / Evaluated.
As a reminder, the A10 (in the 7/7+) had a simplified design, which worked extremely well (i.e., Extreme High Perf).
Apple incorporated fancier & fancier designs in the A11 & A12, which UN-fortunately, they did NOT fully test BEFORE committing to Silicon !
The A13's Perf Controller is almost as good as the A10's !
The Perf Controller in the A12Z would obviously be their latest design, & may be just as Good as the A10's !
Note that this is NOT something the Avg iPhone OR iPad User would ever discover, OR know about.
ONLY those who use Extreme Perf CPU-oriented apps, of which there are very few.
Those who remember Phil's statements about the Perf Controller a few A-series chips back, should have more insight than others into this part of the chip.
But ALSO, ask yourself, why does Apple NEVER mention it anymore ???
You now know the reason !!!