--
Just my 2 cents:
1. DB access - Sure, the DB stuff is usually slower.
What I try to do is minimize DB work and let Perl handle
as much as possible to gain the best performance

2. Modules - As mentioned before regarding Apache and
loaded modules, depends. But as a rule of thumb look
at what the module does for you - usually if you're not
comfortable/experienced enough to write your own module
it's worth using the existing mod even with performance
hit. (The assumption here is that if you do not know
Perl or the problem area well enough to
write a module for your problem, then it's safe
to say the module author may have handled something
you would have missed.)

I'm not trolling here, just saying that if you don't
know it well enough yet trust the module developer and
learn from module code. I've learned a lot
this way, and not just in Perl either.

3. No useful comment.

4. Typically, based on what I've heard, seen
written, and benchmarked myself, OO code TYPICALLY
is slower BUT there are cases where OO is faster
on a module-per-module basis. Depends how it was
written, really.

Plus, is it faster to write code in OO or Non-OO?
I'm a C/Perl guy so for me it's non-OO typically but
depends on problem faced and your mindset (How do you
logically break down the problem?)

Since I was mostly a C guy, it's hard to unlearn
the procedural methods and see things as their
*usually* natural Objects and methods

5. SSI - Is it faster to buy a pre-packaged lunch or
to buy a roll and put cold cuts, condiment, etc. on it?

Static HTML is pre-packaged, canned, and dynamic is your "custom" sandwich.

But sometimes it's better to wait the extra time
so you have your sandwich
"Just Right" (i.e., worth the extra process time)

Hope my rant helps, I know I feel better already.
-felonious