Increase number of emails to be sent via Nesletter

To increase the number emails to be sent for every 5 min:

In app/code/core/Mage/Adminhtml/controllers/Newsletter/QueueController.php

Change the 

$countOfSubscritions = 20;

To

$countOfSubscritions = 100; // whatever number you want

Also in app/code/core/Mage/Newsletter/Model/Oberver.php

Change the

$countOfSubscritions = 20;

To

$countOfSubscritions = 100; // whatever number you want