You're in luck! There are all sorts of methods to benchmark code. I found that there are some excellent explanations on benchmarking in the mod_perl guide.

While the mod_perl guide does talk about mod_perl, much of the information there is relevant to all Perl uses. The first example of benchmarking they give uses the Benchmark module, which you already tried. However, they give other examples using modules like Time::HiRes and GTop. Here is an example of the code you would use with Time::HiRes (copied from the mod_perl guide):

  use Time::HiRes qw(gettimeofday tv_interval);
 
  my $start_time = [ gettimeofday ];
  sub_that_takes_a_teeny_bit_of_time();
  my $end_time = [ gettimeofday ];
  my $elapsed = tv_interval($start_time,$end_time);
  
  print "The sub took $elapsed seconds."
[download]

But the good, juicy information doesn't stop there. They get into code profiling, memory usage, and other goodies -- including the speed differences between method calls vs function calls, along with offering various advice on good coding habits to reduce memory usage.

Feel free to skip any sections that are mod_perl/web specific, if that isn't what you intend to do. Again though, much of what they offer there goes for any code, not just mod_perl and web applications.
-Eric