The toughest (low range) track i have driven would easily be Gee's Arm South/Wheeny Creek
It takes about 7-8hrs to get 5 or 6 vehicles the 6km's out to the lookout and back.
the toughest track i have towed a camper along was actually the silver city highway
We left Tibooburra under grey skies, locals and the signs said the road was open........same story at packsaddle, so we continued on our way.
A few mm's of rain further down south turned the last 50 odd k's of clay based road into an ice skating rink..........kinda fun when you look in the mirror and the trailer is 90 degrees to where your truck is pointing
Kinda scary at the same time though..........