With the bullet you will use, try to figure out what the impact velocity will be at your max distance with each cartridge. You might want to look at what the wind drift will be too. Pick the cartridge that is going to give you what you want or maybe even what will give you more, if you decide to stretch things out further in the future.
I have a Creedmoor, but if I want to push things, I go 6.5-284, and I would use a good solid bottomed brake-I am Partial to Holland's Radial Baffle. Yes, I have several 6.5 short mags in XP's, but for the Encore platform, I would go with the 6.5-284, that is throated properly for the bullet I am using.