Use the gun you are comfortable with and shoot out to 400 yards. Great elk medicine. If you really, really want to shoot farther, there is still no reason to change guns. But if you want to shoot farther couple of questions: Where can you shoot out to 600 yards 2-3 times weekly? That is what it would take as well as having a good chart on wind effects, angle of the shot, etc. Are you a great judge of windspeed or are you taking a windmeter? What about swirls of wind in the moutain? You really that committed? If you aren't, you are doing the game an injustice.

As stated, it is very rare to need to shoot over 400 anyway.