Sorry for the slow reply - life got in the way as it often does.
I did the test located here: https://www.gearslutz.com/board/apple-logic-pro/371545-logic-pro-multicore-benchmarktest.html
(A little old, but still good). My computer could run 180 track reliably! All the cores would max out in the CPU/HD metre, but it wouldn't overload. Again, one core was always a lot closer to peaking on the CPU/HD metre than the rest of them.
When running the 180 track test I turned on the activity monitor and the CPU monitor usage (during playback) was around 1400%! However the memory was only sitting at 2.37 GB whether playing or paused. I therefore doubt that the problem was the RAM - even though I thought it might be.
I may have had background application open, but during the most recent test I had Chrome, Mail, Notes, (Logic X), Steam, and Activity Monitor open, and it could still run the 180 track test session without any problems.
So you are saying it is possible that Logic could overload a few times during a session as it 'settles' or 'works out' how to divide up the cores (if it were a CPU problem) /memory efficiently?
It seems strange that the computer that can work really hard would overload with simple tasks. It usually overloads when I have been tracking software instruments/ or audio with effects on them, and after I have been in the session for a decent amount of time already (say, more than half an hour).