"[Dean Karnazes] ran 3,000 miles (4,800 km) across the United States from Disneyland to New York City in 75 days, running 40 to 50 miles (65 to 80 km) per day, 2011"
I'd agree that it's very unlikely anyone could keep up 90mi/day for very long. If Karnazes can't ...
http://www.badassoftheweek.com/young.html
Cliffy Young is awesome. He's a national hero in Australia.