Benchmark: timing 100000 iterations of do, sys...
        do:  4 wallclock secs ( 2.91 usr +  0.82 sys =  3.73 CPU) @ 26809.65/s (n=100000)
       sys: 441 wallclock secs ( 1.65 usr 19.06 sys + 304.06 cusr 117.50 csys = 442.27 CPU) @ 226.11/s (n=100000)

##</code><code>##

       Rate    sys     do
sys   223/s     --   -99%
do  26110/s 11617%     --

##</code><code>##

use warnings;
use strict;

use Benchmark qw(timethese cmpthese);

use lib '.';

timethese(
    100000,
    {
        do    => sub { do 'script.pl' },
        sys   => sub { system 'perl script.pl' },
    }
);

cmpthese(
    100000,
    {
        do    => sub { do 'script.pl' },
        sys   => sub { system 'perl script.pl' },
    }
);