Would you really worry about saving on petrol in Qatar?!
If you're going to do long drives, you are much better off with a V6... plus a 4 cylinder car may spend more petrol than a V6 on long drives as it is always running on higher revs.
But it all comes down to your budget I guess...
But I think a Prado is pretty heavy to run on a 4 cylinder engine.
Did you test drive both models to assess what you are comfortable with?