Iโd look at a 6mm. Take your pick of x47, Creed, XC or even .243.
If you want to go bigger, probably a 6.5x284 on a new Borden medium action. That would be my pick if big reds are also on the cards.
hard to go wrong really, pick a bullet and the energy you want to deliver at what range; and pick the cartridge and barrel accordingly