We recently did a trip to WA and back, over 8,500 kilometres in 4 weeks.
On the way home we drove from Kalgoorlie to Ceduna without buying fuel in between, 1400 kms, used 259 litres of diesel so about 18.5 L/100. Gotta love the range with having 2 x 140 litre tanks, that was with a tail wind of course and sitting on 100 all the way.
We also did Googs' Track which heads north from Ceduna for nearly 200k to the transcontinental rail line, then we went east to Kingoonya then south via the Gawler Ranges road to Iron Knob, a total of 650k.
All the Googs track was in 4x4 and low range for 2/3rds, the rest of the trip to Iron Knob was dirt roads of varying condition and I still got 19.5 L/100k for this leg. Probably because I never went more than about 80KPH for this leg of the trip.
Video and pics from Googs Track