Range is nice, but in the end you have to go by actual mpg. Use the same fuel pump (to eliminate the variable of when the auto-shutoff occurs), and do at least three tanks of gas, driving as you normally would. Record how much you put in each time, and how far you went, and then determine actual mpg. I keep a logbook in each of my vehicles for this sort of thing.
I've only filled up twice, about 320 to the fuel light. Was sad to see 16.8 on the first; was excited to see 17.9 on the second--until I got in and realized it clicked off at 7/8 full. Doah! I only drive it on weekends so it's going to be another month before I figure out if it has issues, or even figure out exactly what is doing.