Your linked article says 3 minutes and not 5. (And attributes it to starting cups and samba. Ha! Ha!) I'm quite familiar with RHEL, and from the grub prompt it takes less than a minute to boot to gdm on typical hardware, less to a text console. Unfortunately, server systems tend to have a ridiculously long POST. Even so, I've never seen a RHEL server take more than 1.5 minutes from power-on to prompt.