The stats in the link are interesting. I recently discovered the Code::Statistics module (https://metacpan.org/module/Code::Statistics). It tells you the cyclomatic complexity of your code which wikipedia tells me is basically the number of possible paths through your code.

It might be fun to see that run against the Perl core.

I also like looking at the number of lines of code. If your features go up while complexity and lines of code go down -- that could be a good sign.