> firstly array max is 40 - 41 KB which is pushed beyond then

I doubt you measured it right, but $#array=40000 will expand an empty @array to 40001 slots. (well actually even more).

But I doubt it'll allocate space for the included scalars ...(?)

update

see also https://stackoverflow.com/questions/36775922/what-is-the-use-of-preallocating-memory-for-an-array-in-perl

40 KB doesn't qualify as "large" in my book.