I probably have the record for the lowest figure, but I once had the misfortune of riding 315 miles of twisty back roads (slow curves, a lot like the Dragon) with my then-regular group (grey-haired Harley riders). For comparison, we were sore enough after 200 miles that everyone was standing up and bending alternating legs for as long as possible at every stop sign. The road captain was firmly against riding on the highway, believing it was unsafe, and planned out the route in his car, but when he went over schedule (his wife demanded him home at a precise time), he refused to take a break.
If you've experienced a group of old tourers being grouchy when they're in good shape, you have an idea of what this became. I was even riding my '79 GL1000, stock save for a king/queen seat. By the next day, of course, I was proud of my accomplishment, and we all rode together again, though we were vocal that we not repeat that particular level of endurance.
As far as highway mile records, I haven't really done any uninterrupted stint worth mention, but I'm confident I can complete 4-500 on almost any bike without discomfort, given an interstate route plan. I know that plenty of people do at least twice that, otherwise the IBA would be a considerably smaller club, but I'm content to be a chicken and set my limit without wearing a new hole in my ass or strongly regretting the last leg.
'79 GL1000 - first bike, Her Majesty of The Garage
'83 VF750S - doa, free to a good home, extra new parts too
'83 CX650C, '71 CB450, '85 CMX250C
'09 K1300S - so fast, I went 30 years into the future riding it