Interesting! That's the kind of answer I was hoping someone would post. For anyone who's keeping score, here's a benchmark and my results:

#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw(cmpthese);

my $i=0;
cmpthese(-10,
    {
        deref => sub {
            my $aryptr = [qw(Once upon a time in a galaxy far far away
+)];
            if ( @{ $aryptr } )
            {
                $i=1;
            }
            $aryptr = [];
            if ( @{ $aryptr } )
            {
                $i=-1;
            }
        },
        arylen => sub {
            my $aryptr = [qw(Once upon a time in a galaxy far far away
+)];
            if ( $#{ $aryptr } >= 0 )
            {
                $i=1;
            }
            $aryptr = [];
            if ( $#{ $aryptr } >= 0 )
            {
                $i=-1;
            }
        },
    }
);

__END__
           Rate arylen  deref
arylen  95903/s     --   -28%
deref  132418/s    38%     --
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