There will be no standard for an engine with miles. So much depends on frequency of oil changes, quality and viscosity of oil , length of average trips and usage to determine.. At a true 250k 1500 per quart would be nice and reasonable in my mind. . You could be higher or lower at that milage though.
I am not too happy at below a quart of oil per thousand unless there are leaks causing some of it. . I think there are original engines out there that may not add any oil at 250 k original accurate accumulated milage between changes,