I have a 6XC built on a Tikka action, Benchmark barrel, and a McMillan stock. With the 115 DTacs at about 3000-3100 it is a legitimate 1000+ metre shooter. I shot it at Meaford last year and the long targets were in the 1200-1300 range and I made consecutive hits with it there, was very impressed as that was my first time beyond 1000 with the rifle and load.
A big magnum is intriguing, but component cost goes way up, as does recoil and muzzle blast which can make it hard to shoot in a group. But, those big fat rounds are pretty cool and hitting stuff with that kind of authority at extreme range sure brings a smile to ones face!