Actually, there are people using 5.6 because for them, it's the fastest Perl. Perl has the tendency to get slower on new releases; new features, after all, have a price. But it isn't that everything gets slower on a new release -- it's usually some things getting slower, others getting faster, and most things taking about the same time.

For flexvault, things got better. But all we see is the (wallclock?) time of two runs of a single program, with a single dataset, on a single OS, a single machine, and a single set of compilation settings.

Always do your own benchmarking, running programs that you'd run in production as well.

Don't assume that because the version number has increased, the performance has as well.