830 miles in December 1991 coming home from the Gator Bowl. Two other guys and I went to the game and we stayed some distance west of Jacksonville in a motel in Macclenny, Florida. Did the drive home in one day and we had to drop off one of the other guys in Charlottesville, then I had to drop off the other guy at his parents' house near Mount Vernon, then I finished the short remaining drive back to my parents' house where I was staying on winter vacation. Route was I-10 east to I-95, I-95 north to I-64, I-64 west to Charlottesville and then a few local roads to the one guy's apartment near UVA, then I-64 to US-250 to VA-22 to VA-231 to US-15 to VA-20 to VA-3 back to I-95 near Fredericksburg, then local roads in Northern Virginia. We didn't use I-295 around Jacksonville because this was the period when there was an outbreak of people throwing rocks off overpasses.
(Last month my wife and I made a similar drive from Green Cove Springs near Jacksonville. But we didn't have to go through Charlottesville. It knocked about 100 miles off the trip not having to go there, total 734 miles.)
Close second would be 819 miles from my parents' house in Fairfax, Virginia, to Montgomery, Alabama, summer of 1997 when I was working in Alabama for the summer and went home to visit my parents for a week prior to heading south. I was tired of I-85, so I took I-66 to I-81, south to I-40, west through Knoxville to I-75, southwest to I-24, west to I-59, south to I-459 near Birmingham, I-459 around Birmingham, then I-65 south to Montgomery.
The mileage figures may be off by minute amounts due to exiting the highway for gas, food, or toilet breaks.
My longest really fast trip would probably be from downtown Atlanta to Fairfax, Virginia, on December 31, 1995. I had been to the Peach Bowl the night before and wanted to make it home for a New Year's Eve party Sunday night. 653 miles in nine hours, including one gas stop and one food stop and no piss breaks, via the I-85 to I-95 route. I made it from Durham, NC, to Montgomery (560 miles) in 7 hours of driving time once (not including the stop in Atlanta for gas and to hit the Varsity), via I-85 the whole way.