First, it's not the weight of the subprocess, it's the number of invocations that would be problematic. Second, since you are only running your code once, there are all sorts of problems with your benchmark. Use Benchmark to actually test performance. 
#!/usr/bin/perl
use strict;
use warnings;

use Benchmark qw(:all :hireswallclock) ;

cmpthese(20, {
    'Backtick' => sub{`echo plenty of fish` for 1 .. 10},
    'Open' => sub{for (1 .. 10){open my $fh, "echo plenty of fish |"; 
+<$fh>}},
});

[download]
outputs 
           Rate     Open Backtick
Open     9.29/s       --      -1%
Backtick 9.35/s       1%       --

[download]
on my Windows box and 
           Rate     Open Backtick
Open     85.8/s       --     -10%
Backtick 95.7/s      11%       --

[download]
on a Linux server (with iteration count upped to be meaningful).

As an aside, if you are optimizing away milliseconds of overall run time, you probably shouldn't be using Perl.

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re^3: How to capture compile errors from child program? by kennethk
in thread How to capture compile errors from child program? by bulrush

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