I post orders from regional Vic and can totally sympathise - the Aussie Post estimate is approx. 4 days to places like S.A or W.A but it usually seems to take a week/ 5 business days at the least and often longer (the worst I've had is about 2 weeks for delivery).  A few months ago I received some low DSRs for postage time (despite posting same or next business day) - I think from some customers in those states who were judging me on how quickly the post arrived rather than how quickly I posted their items.   I have consequently bumped up the handling time on my listings - I still post quite quickly as always - but the Ebay calculator factors in the extra time so when a customer in S.A, W.A or  N.T etc looks at the listings they have a more realistic estimate of the postage delivery time. 

I had feedback from an S.A customer a few weeks ago and when I realised their package had actually arrived in 4 days for once, I nearly fell off my chair with surprise.