Parallel performance of an OCaml program: ocaml-5.0.0 Vs 4.13.1

I need to share my test data file, that’s the only obvious thing missing.
This is a regular opam package, so installing it should be a matter of opam pin
to the git repository.
I am not particularly interested in people trying to optimize the program.
Rather, I would be more interested by stories of other parallel programs which have an ocaml<5 and an ocaml-5 version.