in reply to what's faster: use or require

I'm just playing with benchmarking, and realised that require costs time at runtime, while use does not.

You appear to be confusing "runtime" with "execution phase". Using the standard definition of runtime (i.e., script start to script exit), both use and require are going to incur costs. You do have a choice in when to incur those costs.

In Section Seekers of Perl Wisdom