I just ran the one you found through paintbrush. The point was that with fuel in the numerator and distance in the denominator, the fuel consumption seems to level off as it approaches infinity, which is to say it doesn't level off.
when i had my 94 civic sedan i would get 33-34 mpg going 95-105 on what would have been 5 hour trips to see a girl i was dating, who is now my wife. and that had the rpms waaay up there. i am actually surprized that your camaro doesnt get better mpg going 65....
don't waste your time or time will waste you