How far to push it past Empty...

[Bakes5]

I averaged 4.5 GPH last summer in my 16 Z3, 440 Raptor, running at ~4800 feet. I don't run much/any weight though as surfing bores me to tears as an all day activity. Our day is typically ski, wakeboard, kneeboard and hydrofoil. Usually 6-10 people in the boat.

Anywho....that's what you can expect for a boat used as an unweighted multi sport boat.

[NAstleford]

We have had the same thing with our fuel gauge.
We were just cursing for probably 15-20 minutes with it ready 2, then 1, then 0 and went a few on 0.
Loaded up and went home. Next time out stopped to fill up and thinking "gawd this is gonna be huge fill up" and it stopped at 22 gal about. Let it sit to vent and put as much as I could in it. Finished at about 25-26 gallons and thought the same thing "it's nice that had some buffer in the gauge reading 0 and actual empty but 20 something gallons is a little extreme." And this was all just cruising, no ballast, no tubing, surfing or anything.