I went at 729 with my 2006 HCH, but had no intention to see where it will die. no spare gas in trunk either... . I filled up about 12.2 gallons or so, to the first click as I always do. I was 90 miles after the empty light came on... I know, I know... but it was no gas station last 20 miles... so, i had to push...

This was freeway most of it... speed was 53-55
Departed from Tustin CA, with full tank, went there (Phoenix AZ), stayed overnight, came back, with the same tank pretty good... It can be done better, I had few speed episodes I did for fun, most likely this car can go way better, and do a 800-850 tank in hot weather on a flat road with constant speed 53-55