Here's a small piece of advice for all who want to upgrade their Perl to the very newest available, but still keep running an otherwise stable Gentoo installation: These three lines are exactly what needs to go into /etc/portage/package.keywords:
dev-lang/perl
virtual/perl-*
perl-core/*
Of course, as always, bugs may be present; what you get as Perl installation is called unstable or testing for a reason. We're looking forward to your reports on our
bugzilla.