With all due respect to Roger, which is significant, I disagree heartily about usage differences. I have never left a stove running between "courses" or anything... that would be a bizarre waste of fuel. I bring enough water to a boil for whatever I need, then turn the stove off. It just makes sense. As for priming fuel, I use ~1-2ml, maybe, to prime. Not significant.
That said, I don't know the actual fuel efficiency difference between WG and isobutane/propane. I think Roger has mentioned a 25% efficiency difference before? However, also consider the weight of the fuel containers--spun aluminum for the WG, steel for the blend...