Read (and heed) what the others above said about premature optimization. But here's what I get for one pathalogical exaple using large hash keys.
greg@sparky:~/perl$ cat hashing_short
#!/usr/bin/perl
my $short="a";
my $long="This is a long hash key"x1000;
my %h;
$h{$short}++ for (1..1000000);
greg@sparky:~/perl$ time hashing_short
real 0m0.376s
user 0m0.375s
sys 0m0.001s
greg@sparky:~/perl$ cat hashing_long
#!/usr/bin/perl
my $short="a";
my $long="This is a long hash key"x1000;
my %h;
$h{$long}++ for (1..1000000);
greg@sparky:~/perl$ time hashing_long
real 2m46.893s
user 2m38.196s
sys 0m0.278s
-- All code is 100% tested and functional unless otherwise noted.