I've always aimed for a "pretty old" version for CPAN modules. When I first started on CPAN, I was taking over an existing module which had 5.6-compatibility, so that was my original default.

As my own skills have improved, I moved to about 5.10, because I use defined-or a lot. And also because 5.10 was easier to have a test suite on Windows (both my personal machines and free CI services).

Recently I've started making use of non-destructive substitution (s///r), though I don't think that's made it into any of my CPAN modules -- if I start a new module, at this point I'm likely to pick 5.14 just to make sure I won't accidentally use that feature without declaring it.

Auditing my handful of modules, two are 5.06, one 5.08, two 5.10, and one 5.12.