Elk are heavier boned, thicker muscled than deer. Given the range of 600-800 yards possible I would feel better served with the 300 wm, and with a chit ton of practice.
In reality, I am guessing around 300-400 yards would be more realistic for a shot given at an elk. My own personal druthers would be the 06' for a minimum period.
I am lost on the fad of using match bullets on game.... A hunter would be just or as better served for hunting such large game with a accubond, swift sirocco.