Having recently returned from my first sheep hunt, I took my 280 Remington, shooting 140 GR accubonds.
I consulted a friend on this matter whom is much older than I and hunts A LOT. It was suggested to go lighter, faster, flatter trajectory.
I can say the biggest thing that helped me was confidence in my ability and a lot of range time. When I ranged my sheep (226 HCD), but with 450' elevation difference, works out to be about 260 yds, I was very confident in my ability to make the shot if I could get a solid rest position. Laying prone and leaning over a cliff slightly, I was rock solid on the rest and felt confident I could make this shot.
the ram was hit, stumbled forward as he was falling and ended up less than 10' from where he was when I shot. Double lung and into the heart a bit as well.
my biggest takeaway was confidence in the shot and my own ability and practice made this happen. For prior hunts (deer and elk) I was confident in my rifle, but I can tell you I have never put this much range time in to prep for a hunt. It paid off!
pick a rifle you are comfortable and confident in, and shoot as much as you can before you go to build that confidence up as much as possible. Determine your comfort level with what distance you can shoot confidently. I practiced at longer ranges, but I set a limit for myself of 350 yards. Sure I could have gone further and knew the bullet drop and such, but I "knew" if it was inside 350, I could seal the deal, no doubt in my mind.