I too am looking to make my XBOX have priority.
I have my XBOX connected directly to the router and it has worked great for the last 6 months or so that I've had the router. Recently, I've noticed that the router seems to be cutting the speed to my XBOX for no good reason. I used to get full bars in games and Netflix at all times and never had any problems. Recently, I can barely even get 1 bar on Netflix and my connection is very bouncy during gaming sessions. There is nobody else using my network when watching Netflix or playing games, so I'm not sure what the issue is all the sudden.
I notice that when I wire my XBOX directly into my cable modem, everything is perfectly fine.
I was hoping that by making my XBOX have priority I could alleviate these issues. I tried using the previous steps listed I get the following error: "'XBOX': Local IP start '##.###.##.###' is not in the LAN subnet". The IP I'm using is what is listed in the settings windows of the XBOX's menus. I have no idea what the error means or how I can correct it. Any help?