Why then did you not bother to write a few lines like:...
Thank you for your answer, hdb, I think I said quite clearly in the original post that I intended to do a benchmark and that I was really looking for some ideas on possibly more efficient ways of doing the splitting, in order to benchmark them along with the ideas I explained. Possibly a Perl function unknown to me, or a use that I did not think about of a function known to me, or a module that I don't know about, whatever. As for the unpack function, I have used it about 5 times in the last 10 years and I had forgotten about the '*' option and I missed it when I looked at the documentation (which, in my humble opinion, could be clearer). Lacking that option, working my way around it was possible but would have made the benchmark less significant because of the added penalty due to this workaround.
I will benchmark all the options that have proposed here and publish the results later on this post.