Iceblock,
Yes, the approximate figures you have worked out are correct.
If you paid upfront or did the salary sacrifice thing you would still end up with the same "cash in hand" so to speak. This is because you would be eligible for a tax refund after paying for your endo up front.
HOWEVER, the salary sacrifice option definitely takes the pain out of it as you don't have to consult accountants, fill out paperwork or even respond to a challenge from the ATO. And of course there's the whole trick of when/how to pay and do the endo to make it a tax deduction.