Dave - what Tonto said about the slope. And by that measure, in order to get a 5" drop you'd need to be 20 feet
from the drain. I don't think so.
One thing to keep in mind is that if the floor is square and drain centered, the slope is equal all the way around. But if the drain is off-center or the floor is not square it's a different story. the 1/4" per foot is from the drain center to the wall furthest from the drain. yes, that means shorter sections of floor have more slope. The goal is to get the perimeter of the floor at the same height all the way around.