I have run multiple 5 gallons fills in a 15 gallon tank with no appreciable increase if FE. It does accelerate better but it was a hassle to fill up every 2-3 days. There is no doubt that lighter equals better FE but I don't think that this is something that will show up on the fuel gauge. Kind of like getting rid of the spare. In the long run I want to get home. YMMV.
