Always thought the tank in these(3rd gens) were 71 litres?

You get around the same as me on a empty fill of about 57-60 litres, this is normally when the light comes on in the GTV.
So this would give about 10litres or so of useable fuel before bone dry. So 600klms(going on your odo) with roughly a hundred or so to go(10l/100klms) before stall, is awesome yeah?

Im averaging around 10.3 in the 3.5 GTV. This has been with the climate on auto @ 20oC with a few days on flatout. And im far from a conservative driver...... This includes two trips to NSW on the hume on around 115km/h loaded with 3 kids, 2 adults, luggage etc.
Shits on any falcon or commy ive had or been in.