The following are also interesting benchmarking applications implemented in Perl:

HTTP::WebTest
The HTTP::WebTest module (available from CPAN) runs tests on remote URLs or local web files containing Perl, JSP, HTML, JavaScript, etc. and generates a detailed test report.

HTTP::Monkeywrench
HTTP::Monkeywrench is a test-harness application to test the integrity of a user's path through a web site.

Apache::Recorder and HTTP::RecordedSession
Apache::Recorder (available from CPAN) is a mod_perl handler that records an HTTP session and stores it on the web server's filesystem. HTTP::RecordedSession reads the recorded session from the filesystem and formats it for playback using HTTP::WebTest or HTTP::Monkeywrench. This is useful when writing acceptance and regression tests.

Many other benchmark utilities are available both for free and for money. If you find that none of these suits your needs, it's quite easy to roll your own utility. The easiest way to do this is to write a Perl script that uses the LWP::Parallel::UserAgent and Time::HiRes modules. The former module allows you to open many parallel connections and the latter allows you to take time samples with microsecond resolution.