All the ethics stuff about extreme range hunting has been said before, but I'll just chime in here.
1000 yards is a hell of a long way. I've shot competetively against the very best in the world at that range, and I can tell you that it is not a joke. Without a doubt, you can hit an animal in the heart at that range with a tricked-out rifle, a huge amount of skill, and the conditions in your favour. But the odds are against making a one-shot kill like that in a hunting situation, where you don't have a series of range flags and a spotting scope set to the right focus to catch the mirage.
If you're serious about taking a large animal at 1,000, I'd choose the .300 Winchester as a reasonable minimum. With a 180 or 200-grain Accubond and a stout load, it'll have the horsepower to drop even a moose at that range. One of the Ultramags or the Lapua would offer more power, for sure. But at this range, NOTHING is more important than accuracy. Above all else, you must have a rifle that is capable of consistently shooting groups that are LESS than 1/2 m.o.a. Remember, at 1,000 yards, 1/2 m.o.a. translates into five inches. Even world-class shooters are lucky if they can hit the x-ring half the time at 1,000, and the x-ring at 1,000 yards is about 10 inches in diameter.
This is just some food for thought.