I did this test:

use Benchmark qw(:all);
use File::Slurp;

$file_slurp = sub { $file = read_file('arq.pdf', binmode => ':raw') };
$read       = sub { open $file, '<', 'arq.pdf' || die $!; read $file, 
+$data, -s 'arq.pdf'; close $file; };
timethese(1000, { file_slurp => $file_slurp, read => $read, });
cmpthese(1000, { file_slurp => $file_slurp, read => $read, });
[download]

I got this results:

Benchmark: timing 1000 iterations of file_slurp, read...
file_slurp:  1 wallclock secs ( 0.43 usr +  0.31 sys =  0.74 CPU) @ 13
+51.35/s (n=1000)
      read:  6 wallclock secs ( 4.88 usr +  0.44 sys =  5.32 CPU) @ 18
+7.97/s (n=1000)

             Rate       read file_slurp
read        192/s         --       -86%
file_slurp 1333/s       595%         --
[download]

I see that file_slurp in this case is the best option. I've used a 80k file with 1000 lines and 79 columns.

Using a 2.5Mb pdf file the results were different:

file_slurp: 44 wallclock secs (15.99 usr + 26.40 sys = 42.39 CPU) @ 23
+.59/s (n=1000)
      read: 23 wallclock secs ( 9.12 usr + 13.67 sys = 22.79 CPU) @ 43
+.88/s (n=1000)

             Rate file_slurp       read
file_slurp 23.6/s         --       -46%
read       43.6/s        85%         --
[download]

I this case File::Slurp was slower than read(). I see that File::Slurp has a binopen mode. After changing to binmode:

file_slurp: 46 wallclock secs (16.01 usr + 26.25 sys = 42.26 CPU) @ 23
+.66/s (n=1000)
      read: 25 wallclock secs ( 9.00 usr + 13.91 sys = 22.91 CPU) @ 43
+.65/s (n=1000)

             Rate file_slurp       read
file_slurp 23.7/s         --       -46%
read       43.5/s        84%         --
[download]

I think in bigger files read() has better performance than File::Slurp... I don't know why but I hope it helps :-)