My favorite long range caliber is 6.5 x 284. My longest antelope kill with it was 970 yards. Fortunately the wind gods were on my side that day. You can have the best velocity, BC and sub MOA rifle but with a varying crosswind it is all for nought.
There are antelope around me, but the wind at this high elevation is always in the form of many whirlwinds of various sizes. At times, a bullet could go through several of them at 400 yards. There’s no way to estimate winds here for long range shots.
6.5 x 284? That’s a long cartridge, almost a foot. Where do you get the brass?