Testing efficient way of loading customer data

loadcustomer.php

<?php
require_once '../app/Mage.php';
Mage::app();
umask(0);

$customerId = 575420;
$start = microtime();
$memory1 = memory_get_usage();
$customer = Mage::getModel('customer/customer')->load($customerId);
$firstname = $customer->getFirstname();
$lastname = $customer->getLastname();
$memory2 = memory_get_usage();
$end = microtime();

echo "<p>";
echo $firstname . "<br />";
echo $lastname . "<br />";
echo "Start: $start, End: $end => " . ($end - $start) . "<br />";
echo "Memory Start: $memory1, End: $memory2 => " . ($memory2 - $memory1)/1024 . "KB <br />";
echo "</p><p>";


$start = microtime();
$memory3 = memory_get_usage();
$customer = Mage::getModel('customer/customer')
    ->getCollection()
    ->addAttributeToSelect('firstname')
    ->addAttributeToSelect('lastname')
    ->addAttributeToFilter('entity_id', $customerId)
    ->getFirstItem();
$firstname = $customer->getFirstname();
$lastname = $customer->getLastname();
$memory4 = memory_get_usage();
$end = microtime();

echo "<p>";
echo $firstname . "<br />";
echo $lastname . "<br />";
echo "Start: $start, End: $end => " . ($end - $start) . "<br />";
echo "Memory Start: $memory3, End: $memory4 => " . ($memory4 - $memory3)/1024 . " KB<br />";
echo "</p>";

First call:
Time: 0.018482
Memory: 1875.171875KB

Second call:
Time: 0.001501
Memory: 122.3671875 KB