If your website has decent volume and you are using mod_perl with lots of dynamic content (hopefully with templating), then you probably want to be using a reverse proxy setup. See this guide (particularly Adding a Proxy Server in http Accelerator Mode) for an explanation of what it is and what the benefits are. From your point of view the big benefit is that a mod_perl server ties up a lot of memory, so that configuration allows you to have fewer big mod_perl processes all actively producing content, and let the proxies take care of returning data over the slow wire to the browser.

After you do that then the answer to your rhetorical question about why it matters how fast the mod_perl executes is that improving speed there will reduce how many heavy mod_perl children you need for a given load, which will save on memory and CPU requirements (which translates into the number of webservers that you need).

Another detail. What I (and many other people) dislike about Zope has nothing to do with templating. In fact I dislike the same thing about the way that this website is designed and the way that many Smalltalk and/or Lisp projects are run. And that failing is that Zope wants to store an opaque binary image (in its case in an object database) that includes HTML and code. That immediately takes the wonderful world of filesystem-based tools (everything from grep to revision control tools) and throws them out the window. Work its way and you have to reimplement all of them, and learn the new toolset just for Zope. And if it gets them wrong, then enjoy trying to manage your releases (eg roll code forward and back).

This design decision is completely orthogonal to whether or not to use templating, and it seems that you missed it.

I won't comment on your other points since I mostly agree with you.