Testuję tworzenie tablicy SplFixedArray z dniami tygodnia i otrzymuję następujące wyniki:

<?php

$days = new SplFixedArray(7);

$days[0] = "Monday";
$days[1] = "Tuesday";
$days[2] = "Wednesday";
$days[3] = "Thursday";
$days[4] = "Friday";
$days[5] = "Saturday";
$days[6] = "Sunday";

echo memory_get_peak_usage() . "\n"; //Returns 327688
echo memory_get_usage() . "\n"; //Returns 327140
echo memory_get_peak_usage(true) . "\n"; //Returns 524288
echo memory_get_usage(true) . "\n"; //Returns 524288 

Z tradycyjnymi tablicami:

<?php

$days = array();

$days[0] = "Monday";
$days[1] = "Tuesday";
$days[2] = "Wednesday";
$days[3] = "Thursday";
$days[4] = "Friday";
$days[5] = "Saturday";
$days[6] = "Sunday";

echo memory_get_peak_usage() . "\n"; //Returns 327528
echo memory_get_usage() . "\n"; //Returns 326820
echo memory_get_peak_usage(true) . "\n"; //Returns 524288
echo memory_get_usage(true) . "\n"; //Returns 524288

Czy to ma dla ciebie sens?