This is premature optimisation gone mad! For most purposes for speed to be a factor in this decision the array would need to contain of the order of 1 million entries.

Actually, significant differences start at around 200,000; and as someone who regularly does similar processing with 10s and even 100s of millions, knowing what works quickest whilst avoiding unnecessary memory growth is important.

And unless you have some psychic insight to the OPs application, you have nothing on which to base your conclusions, so it is they that are "premature".