Well, I've got two AU and the Ute uses more fuel on the highway. Yes there is a some weight difference. But the real issue as pointed to by many is the aero.
Tske a look at the smoothness of the underside of the sedan and it's not too bad. Under the rear of the Ute it is all over the shop with massive rises and falls. Under vehicle aero is much more important than people give credit for!
To the
OP, if your looking to buy, now is a really good time to get into a new Falcon!
I've just started looking myself.