For 1K big game I would recomend the 338 EDGE if you can handle the weight and recoil.
If not, I would look long and hard at the 300 WSM
for 700-800 yard big game.
Both the 6.5x284 and the 300 RUM are very hard on barrels. For a new comer, this can lead to alot of frustration as well as expense. If you go with less of a barrel cooker, you can learn the ropes of LR shooting without the frustration of a changing barrel and the expense of a new one every year or two depending on how much you shoot.