It seems to me that the only way to know how far you can go, after the warning comes on, is to run till you are out of gas. I've only done that in my truck (which had 2 tanks) where I could switch over. But it really messes up your fuel injectors to run to the bottom of the tank.
When I flew airplanes in 3rd world countries, we always filtered the gas through a chamois. That gives you the best chance of getting clean fuel.
The worst thing you can do is go into a gas station when you see the big truck dumping gas into the underground tanks. You're sure to get crap in the fuel even several minutes after they are done.
I like to put about 2/3 tank full and refill before the warning. I hate walking.
008 ZX14R Ninja ... Midnight saphire blue with custom lightning bolt paint job, Kenny Rodgers KRTuned mufflers, Corbin custom seat, Marchesini wheels, Dunlop Qualifiers, Dyno Jet PCIII, custom FAICS map, Dyno Jet Ignition Module, K&N Air Filter, Supersprox 44 tooth sprocket, Zephyr 16 front sprocket, EK chain, TRE008, MRA windscreen, Race Railz frame sliders, Sato Racing axle sliders, ST Machine brake & clutch levers, Engine Ice coolant, Muzzy aluminum fan, ceramic coated headers and midpipes (cat removed), Vortex Rear Sets , Pro Comp Stearing Damper, Pro Grip Gel handgrips, Gen Mar clip on risers, Dowco tank bag, and a Rumble fender eliminator.
Removed GPS.
2005 Harley Davidson Dyna Low Rider, 1442 CI fuel injected, 65 HP, lots of chrome with 24K gold overlay detailing. Sure is pretty!