I've killed game with both rounds. My example is very small indeed, but; To "me" I felt the 6.5/284 was a more emphatic killer and this was with the lighter weights too ( 129 in the 260 and 120/125 in the 6.5/284) 3200 with either of the Noslers was like a knife through the wind, stretched string trajectory ( zeroed +1@100, hold on hair to 300+) I am not a long range hunter, "if" long range doesn't start until 500yds away, though I will shoot that far to check my ability to hit , say, a wounded animal, I have only killed right at 5 head of game from 350 to 375, could not get closer and it was important to me at the time; and one unlucky cottontail at 405yds, ha. All the rest were 250yds and much closer. I am not a good judge of the wind so the 140s were never in my quest. The rifle was a short action Mod 700 in a Classic stock, started out with a $90 Adams & Bennett Midway barrel in .260, 24" Sporter barrel. One hunt with the 260 round, then reamed to the 6.5/284. My only problem was it didn't want to feed the last round right. I used necked down Winchester 284 brass which I could run hotter than the new Hornady and Norma. Admittedly, I could have come close with the 260 AI, but I just "had to see" what the fat little case would do, ha. Though I have had both the 300 RUM and 7mm RUMs made up and scoped for 900yds, I could never make myself shoot at game that far, so sold them off. I'm too old and bolted together to walk way over there and pack him out...that's "after" I managed to even find him if he ran out of sight. When you get where you though he "was" it might hasve been 50yds higher or lower, just hope you have a good blood trail. I don't like that.