TIL that I can use Perl's Benchmark module to time and compare the performance of different commands in an OS-agnostic way, ie as long as Perl is installed.
For example, to benchmark curl, wget and httpie you could simply run:
See also: The shell's own times command (where available), and/or the external command time, which is the fore-runner of all of these.
Those won't run a command a number of times or provide a pretty table like Perl's benchmarker will, but if you want to roll your own, those would be the place to start.
(I'm a big fan of Perl, but know that not everyone's ready for it yet!)