For this operation, one very simple optimization would be swapping from a for to a while loop since Foreach Loops need to construct the list before beginning iteration. threads is also a fairly simple way to improve performance. Here is a simple benchmark, showing a 38% speedup using a while loop and two threads. Note the speedup is not higher because creating threads involves overhead.

Threading in this case does not make sense - the overhead in starting a thread exceeds the performance boost. For loops with range operators are automatically transformed into efficient C-style loops internally by Perl. But you should really be using the Stirling_approximation and only storing the log of your value to avoid overflow.

#!/usr/bin/perl
use strict;
use warnings;
use Benchmark qw':all :hireswallclock';
use threads;

cmpthese(10, {
    'while' => sub {
        my $i = 230000;
        my $k = 1;
        while ($i <= 900000) {
            $k *= $i++;
        }
        },
    'for' => sub {
        my $k = 1;
        for (230000 .. 900000) {
            $k *= $_;
        }
        },
    'threads' => sub {
        my $k = 1;
        my $thr2 = async {
            my $k = 1;
            my $i = 565001;
            while ($i <= 900000) {
                $k *= $i++;
            }

            };
        my $i = 230000;
        while ($i <= 565000) {
            $k *= $i++;
        }
        $k *= $thr2->join();
    }
});
[download]

outputs

          Rate threads   while     for
threads 3.09/s      --    -29%    -38%
while   4.33/s     40%      --    -13%
for     4.96/s     60%     15%      --
[download]

And if you look at the results from these multiplications, you have likely exceeded the maximum value representable by floating point on your machine.

Update: Need caffeine, read my Benchmark results backwards, fixed above.