simpson desert and canning stock route

Have you checked the consumption city and highway cycles before and after installing the turbo. If you have, then I suspect you would already have the answer. As for cross-country off-road, YES in hard/heavy (sand/mud) you will always consume more fuel. It's logical, an engine working lightly, not towing and running at minnimum revs will be more econmoical than one that is fully loaded or towing negotiating off-road conditions.

More power only comes from more fuel and air.

If you can keep off the throttle and only use the same power as the non turbo engine, same fuel consumption.

However, (isn't there always a but), I have found that with careful tuning of the fuel pump, I am blowing less smoke, and getting better economy with the turbo, so assume more air is meaning better combustion. But the difference to fuel consumption is marginal.

Patience grasshopper. I am sure you will find your question posted several times in this forum in other threads, and answered there as well. :-)

When in the dune country, the secret to a successful crossing is driving technique. Do not go like a bull at a gate, but slow as it goes and use your vehicles torque. Correct tyre pressure will have a great bearing on driving as well.
The people that go at break neck speeds are the ones that do all the damage, cutting up the tracks and using more fuel and have tyre pressures far greater than they should be.

Cheers

Stephen