A buddy went on a guided Elk hunt and the guide told him to use the guides Christiansen in 300 Winnie. They spotted a large bull, ranged it at 600yds. The guide told him to adjust up 15 clicks and hold dead on. One shot, one kill.
I don’t know the glass he used but the guide knew his Christiansen rifle, where it was sighted, adjusted and it put the bullet right there after bouncing around in a RZR then hiking. That work for me.
As far as a RUM vs Winnie I would go a Winnie.