@$ra = @$ra[0..$index-1], $elem, @$ra[$index..@$ra-1];

##</code><code>##

    splice(@$ra,$index,0,$elem);

##</code><code>##

cmpthese (5000, {
    radiantmatrix => sub { my $array = [1..1000]; insert_array_elem1($array,1,$_) for 50..100 },
    use_splice => sub { my $array = [1..1000]; insert_array_elem2($array,1,$_) for 50..100 },
});

##</code><code>##

                Rate radiantmatrix    use_splice
radiantmatrix  467/s            --          -83%
use_splice    2762/s          492%            --