923 yds (or 928, can't remember) on a New Mexico Pronghorn, 6.5 CM 147 gr factory Hornady ELDM. Perfect conditions, big open valley between his herd and us with no significant cover. 2-3 mph L to R wind. Had a huge flat rock to get prone on.
Lay and watched him feed towards us, when he turned perfectly broadside and stopped, nailed him. Down in his tracks with a spine shot (was aiming for high shoulder).
If I had it to do over I wouldn't. I just spent a couple days at a shooting course and was consistently hitting at 1000 yds in worse conditions than we had. I'd been training and shooting hard all summer and was probably shooting the best in my life, but hit him 1 moa further back than I intended as I under-called the wind.
Still, it was as good of conditions as I could have hoped for with a spotter I trusted helping me gauge the wind. Bottom line: that's probably the longest shot on game I'll ever take. I've stepped up to a 6.5 PRC and 300 PRC, continued to practice, but even under ideal conditions I think it's too far for me (and especially a 6.5 CM). YMMV.
However, I am a big believer in shooting instruction and practicing on steel in similar conditions out further than you intend to hunt. Really helps you know your capabilities.