On a recent Iron Butt Saddle Sore 1000, I did 1043 miles in just over 18hrs (Shamrock, TX, to Acworth, GA). That's an average of 57.5mph. Speeds were around 80mph (average) for most of the time during the day and then dropped to around 70mph after dark. I lost about 45min sitting in a dead stop about 15 miles from my final stop (broke down car in a construction zone north of Atlanta.