I think there are massive diffences in one persons "empty" and other peoples. Some people fill up when there is a quarter left, some when the light comes on, others when the ------ comes up.
I used to do 500 miles a week in mine and 400+ miles from a full tank before the light came on was very hard to achieve even driving conservatively.
I once, out of neccessity, did 360 miles untill the light came on and then 70 miles on the --------- but i had everything turned off and was riding the clutch downhill at every opportunity