RE: 308 or 243?
Any of these mentioned is great, the 308 has spawned many great cartridges. The 708 is a great choice, I would stick with 140 gr Ballistic Tip type bullet (any of half dozen from various manufacturers). While all my terminal ballistics knowledge says an exit wound is where its at, having dug out dozens of ballistic tips from under the hide on the off side, they may come apart and not punch the other side, but Jesus H do they kill like lightning!! A 120 gr out of a 260 kicks very little and kills all out of proportion to its paper ballistics.