Very simple performance comparison - arrays vs objects (PHP 5.3.6)

gistfile1.sh

# php -v
PHP 5.3.6 (cli) (built: Mar 17 2011 20:58:15)
Copyright (c) 1997-2011 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies

# echo '<?php $s = array(); for($x=0;$x<1000;$x++){ $s[] = array("name"=>"Adam","age"=>35); }; echo memory_get_peak_usage(); ' | php
655040

# echo '<?php $s = array(); for($x=0;$x<1000;$x++){ $o = new ArrayObject; $o->name = "Adam";  $o->age = 35;  $s[] = $o;} echo memory_get_peak_usage(); ' | php
887984

# time echo '<?php $s = array(); for($x=0;$x<100000;$x++){ $o = new ArrayObject; $o->name = "Adam";  $o->age = 35;  $s[] = $o;} echo memory_get_peak_usage(); ' | php
61010784
real    0m1.448s
user    0m1.208s
sys     0m0.231s

# time echo '<?php $s = array(); for($x=0;$x<100000;$x++){ $s[] = array("name"=>"Adam","age"=>35); }; echo memory_get_peak_usage(); ' | php
33647944
real    0m0.525s
user    0m0.429s
sys     0m0.092s

For information, you will get very different results if each Array/Object is different :
Array("name"=>"Adam$x","age"=>$x)
MyArrayObject("Adam$x", $x)

A quick test for PHP 7.2 https://gist.github.com/charrondev/be56ef53e0408b959eff6d2d911e8c1e

Type	Memory Usage	Real execution Time
Arrays	46,191,568	0m0.137s
Classes	20,537,808	0m0.129s