So I've been told that Supra's drink petrol like its water.
Well I can give you the exact answer your looking for.
I get a good 425KM running on a full tank of Premium 98 before the empty light comes on. I believe it could do at least 450KM before I start running on fumes, but I tend not to risk it, although I do plan to run completely dry until my 34 becomes dehydrated to the point the engine shuts off just to see the MAXIMUM it can do on a full tank.
Gotta get myself a Jerry can first.
But to answer your question, 425KM on full tank of 98. Auto R34 25GT with RB25DE, no mods. Costs me about $140 a week though to run, since it's my daily and I drive it to city and back most days.