I figure that the K4 on my AR makes it a good 200-yard coyote gun. Were I serious about jackrabbits and coyotes beyond 200, I'd likely go to a 3x9. It's not difficult to find a running critter at 3X, at around 40 to 50 yards.
In my walking-hunting, I always had my 3x9 set on 3X. Never a problem, and even 3X is plenty good for Bambi at 350 yards--as I found out.