While I'm not really qualified to have an opinion on the issue, you might consider looking for another "natural" breakpoint: specifically the lowest version that gets installed by default among various Operating Systems. I don't know what version that might be, but looking at your 'hoops' argument, I think it feels similar--when people set up a box, they're going to get some minimum version X, and if they need to install an older version to support some application, they'll have a similar circus act to follow.
I don't know if that would give a different result than your suggestion of 5.12 or not, I'm just offering another thing to think about. Personally, I like 5.12 as a minimum version because I use // quite a bit and state occasionally.
- I've never been primary production support on large systems, so while I'm somewhat of an old hand at using perl, I typically run the version that comes by default when I install a *NIX distribution or Cygwin on a Windows box.
- Again, I don't support production systems, so I just grab a distro that I'd like to use and go with it.
When your only tool is a hammer, all problems look like your thumb.