I think my idle speed is around 600 to 800 RPM. Can't remember.
As far as rolling down the hill; I wonder if your brakes are dragging. However, my XF doesn't roll back too quick when I'm on a hill, the guy behind me is too close, and I have to ease the clutch out. I'm glad of that. Maybe that's just the way these cars are.
Also, I think our cars are geared pretty low, so they might slow down more than other cars.