My site is about 80,000 lines of mod_perl code.

I wrote a relatively large framework, with many homegrown perl modules, about five years ago.
It uses a database, image generation modules, a big mathematical engine that I wrote (that "shows work", unlike popular third party packages), etc.

All pages of my site are dynamic and it is very image heavy due to math formulae.

I can say two things:

1) It is relatively fast, serving pages in 0.1 seconds or so

2) Despite the quantity of code, and its age, it is still very maintainable and understandable (to me).

If I was to make a choice again, I would go with mod_perl again. With Perl, I can "stand on the shoulders of giants" like Lincoln etc, and use the brilliant stuff they provided to serve my users.