The use constant pragma implements constants as inlinable subroutines, but “In the current version of Perl, list constants are not inlined...” (constant, v5.18.0). Benchmarking on my version (Strawberry Perl v5.16.0) actually shows a significant reduction in speed:

#! perl
use strict;
use warnings;
use Benchmark qw( cmpthese );

use constant LABEL_ARRAY => qw(Title Section Subsection Class Category
+ Degree Attempt CountOfCounts);
my          @label_array =  qw(Title Section Subsection Class Category
+ Degree Attempt CountOfCounts);

cmpthese( -1, { array => \&array, constant => \&constant } );

sub constant
{
    my $sum  = 0;
       $sum += length for LABEL_ARRAY;

    return $sum;
}

sub array
{
    my $sum  = 0;
       $sum += length for @label_array;

    return $sum;
}
[download]

Output:

23:59 >perl 660_SoPW.pl
             Rate constant    array
constant 155802/s       --     -70%
array    511619/s     228%       --

 0:01 >
[download]

:-(

Hope that helps,