In my wife's 2008, I just use the Motorcraft synthetic blend 5W-20 oil and a quality filter every 5000. About 60% highway miles and with 80K on it now the oil still comes out just a light brown color. I am sure it could go longer, but every 5K is easy to remeber and keep track of. Plus doing oil change myself it is relatively low cost ($20 range).

Royal Purple is excellent oil. I think overkill for an Edge. If you really want to understand the oil change interval, you need to do used oil analysis and it will let you know when the oil is due for change.