I rode from Stockholm to Eastbourne without any rest breaks (just petrol, coffee & pee breaks) in 1997, that took about 28 hours and is approx 1200 miles. I had actually started the day before in south east Finland, but had a couple of hours sleep on the Turku to Stockholm overnight ferry.
I did it again in 2011, but took an overnight break to the west of Copenhagen. I think my mileage on the third & final day of that trip was just short of 900 miles. I was aiming for Witney in Oxfordshire on that occasion but my bike (Harley Softail Classic) broke down at Beaconsfield services.
I am aware of the IBA and their rules, but 1000 miles in 24 hours is tough going!