I used my Howa Mini in 6 ARC to kill a small bear this spring. 400ish yard shot, 103 ELDX, left side impact a few inches behind center of center, exited out the right rear quarter. He dropped on the spot despite the sub-optimal bullet placement. This is my only experience with 6 ARC on animals so far, but there are quite a few 6 ARC kills in the 6mm for everything thread.
As a side note, in an effort to maximize opportunity and limit effectiveness, "restricted weapon" hunts have started to pop up in the west. Things like the use of scopes and semi-auto rifles aren't allowed in these units. Right now these units are not very widespread and mostly experimental. With the current demand for tags, units like this might become more common in the future. Just something you might want to consider if you are going to build your "one gun" for western hunting on a semi-auto platform.