$ uname -a
Linux hogehoge 2.6.32-431.20.5.el6.x86_64 #1 SMP Fri Jul 25 08:34:44 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ cat /etc/centos-release
CentOS release 6.6 (Final)
$ php --version
PHP 5.6.2 (cli) (built: Oct 16 2014 09:08:04)
Copyright (c) 1997-2014 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2014 Zend Technologies
$php /tmp/array.php
----- array_unshift() -----
time:286.2655980587
a1[0] = 99999
----- array_reverse() -----
time:0.29395484924316
a2[0] = 99999
$ php /tmp/array.php
----- array_unshift() -----
time:297.66237282753
a1[0] = 99999
----- array_reverse() -----
time:0.061238050460815
a2r[0] = 99999
$ php /tmp/array.php
----- array_unshift() -----
time:286.67047691345
a1[0] = 99999
----- array_reverse() -----
time:0.079139947891235
a2r[0] = 99999
やらなくてもなんとなくわかってったけど、$array[]で後に追加していって最後にarray_reverse()したほうが断然速い。