On just under 8.7 gallons of 93 octane, I drove 448.6 miles over the past three days. According to the ScanGaugeII, I'd used 8.4 gallons, and that's the amount I'd put in this morning before the pump shut off (I squeezed in another 0.3 gal). Since my SG is set to assume I gave a 9-gallon tank, in never exactly sure to what extent I can trust it. The car's gauge, also a bit unreliable, was on 0.0. I've noticed lately that it does a poor job of reading my last 1.0 gal, which disappears much faster than expected based on the other 7.7 gallons measured by the gauge. So when my 1.0 gal light shows up, I prolly have 0.6 gallons left before it reads 0.0.
To achieve over 50 mpg, I drove an average of about 53 mph and did most of my driving on the highway during off hours.