Ken replied:

Hi Luke. I would think it would be about mid way between max torque and max power,maybe 2800 revs. Would that be about 100 kph in this vehicle? Regards Ken.

Andrew replied:

Luke, Kens reply is pretty spot on, but remember, that historically someone once ate an apple they shouldn't have, so the world is not perfect, so we have to contend with wind resistance, and with a vehicle, shaped a bit like a cross between a bashed crab and a brick, above about 85-90 km/h starts to invade fuel consumption as you push the stuff around the vehicle.
And it gets worse, as this friction is not directly proportional to the increased speed, bit like friction loss with fluids, has a 4 times factor, from memory, any rocket scientists may help us here...
I find that above 90 km/h, the fuel consumption starts to increase, at 100km/h I get about 10-10.5 km a litre from my rodeo t/d.
above 100, and it likes to drink, and i think that would be similar with most 4wd's.

grahame replied:

only had my turbo diesel since early february
coolumn to brisbane motor has a sweet spot at 2750
revs which in mine is 100 klms/hr.two successive trips got 8.85 ltrs/100km & 8.67 ltrs/100km third trip 3000 revs got 9.46 ltrs/100 km.with my caravan behind sweet spot seems to be 2600 revs
which is 92 kms/hr.darling downs to coolum 11.3 ltrs/100 km .coming home which involves more climbing got 12.57 ltrs/100km.with van on hit a hill at 90 it dies to 80 & hangs on. but if i accellerate to 95+ coming to hill it hangs on at 90.so at this stage i will operate in 2500 to 2800
range.have better figures after darwin trip
range