Mine has been pretty consistent around 7,000 to 7,500 miles.
Ford put a number of these engines to work in real life jobs prior to actually shipping the truck, They brought the engines back in at various mileage intervals and looked at the oil and found that most of these trucks can go 9,000+ per oil change. They set the oil life minder to a interval shorter than engineering data suggested was safe. I don't know if I could find that discussion, I was reading it back in the summer of 2010.
But based upon that discussion and my oil analysis that I have sent off for testing, I'm comfortable sticking with the 7,500 mile interval.