test.php

<?php
define('RUN_ITERATIONS', 100000);

function avg($array) {
    return array_sum($array) / count($array);
}

function ifseta($arr, $k, $default = null) {
    return isset($arr[$k]) ? $arr[$k] : $default;
}

$array = range(0, 1000);

$issetTimes = array();
$ifsetaWithDefaultTimes = array();
$ifsetaTimes = array();
$ifsetaNoFuncTimes = array();

$j = 100;

while ($j) {
    $i = RUN_ITERATIONS;
    $time = microtime(true);
    while ($i) {
        if (isset($array[rand(0, 2000)])) {
            $i--;
        } else {
            $i --;
        }
    }
    $issetTimes[] = microtime(true) - $time;

    $i = RUN_ITERATIONS;
    $time = microtime(true);
    while ($i) {
        if (ifseta($array, rand(0, 2000))) {
            $i--;
        } else {
            $i--;
        }
    }
    $ifsetaTimes[] = microtime(true) - $time;

    $i = RUN_ITERATIONS;
    $time = microtime(true);
    while ($i) {
        if (ifseta($array, rand(0, 2000), 5)) {
            $i--;
        } else {
            $i--;
        }
    }
    $ifsetaWithDefaultTimes[] = microtime(true) - $time;

    $i = RUN_ITERATIONS;
    $time = microtime(true);
    while ($i) {
        $key = rand(0, 2000);
        if (isset($array[$key]) ? $array[$key] : 10) {
            $i--;
        } else {
            $i--;
        }
    }
    $ifsetaNoFuncTimes[] = microtime(true) - $time;

    if (0 == $j % 10) {
        echo '.';
    }
    $j--;
}

echo PHP_EOL,
    'Isset:           ', avg($issetTimes), PHP_EOL,
    'Ifseta:          ', avg($ifsetaTimes), PHP_EOL,
    'ifseta(default): ', avg($ifsetaWithDefaultTimes), PHP_EOL,
    'ifseta(native):  ', avg($ifsetaNoFuncTimes), PHP_EOL;