use Benchmark;

@in = (1,2,3,4,5,6,7,8,9,0);

timethese ( 100000, { 
    'C-style' =>
            'for my $i ( 0 .. $#in ) { 
                $i % 2 ? $out2[int($i/2)] = $in[$i] : $out1[$i/2] = $in[$i] 
            }',
    'push'  => 
            'for my $i ( 0 .. $#in ) {
                $i % 2 ? push @out2, $in[$i] : push @out1, $in[$i];
            }' 
        } );

__DATA__
Benchmark: timing 100000 iterations of C-style, push...
   C-style: 13 wallclock secs (12.97 usr +  0.00 sys = 12.97 CPU) @ 7710.10/s (n=100000)
      push: 18 wallclock secs (18.79 usr +  0.00 sys = 18.79 CPU) @ 5321.98/s (n=100000)