I am able to load to 3.40" in my mag. I run a hex coated 208 grain ELD to 2750 fps with RL 17 in Win brass. I was pushing a 215 to 2650 fps with the same powder with out hex coating. I would think you could get 2600 fps pretty easy and that would get you to 800. As far as stability, you need to consider the elevation you will be hunting at. And honestly I would consider that when doing load development as well. Things change the higher up you go.
Having said that, a 7 mag or 300 mag makes things so much easier past 500 yards.