New guy here, you might want to try a 6.5 grendel, i"ve been using one for 4 years,yotes at 700 deer at 400 web site is back up worth alook...
I'd go with a 6.5x284 Norma over a grendel or creedmore any day of the week. They have a slightly fatter casing so you have a ton more options for loads and bullet weights.
But in general, any of the 6.5s are lethal on whitetail up to 850 yards. That's pretty **** impressive. Consider this... most competition palma, and long distance rifle competitors use 6.5mm or 6mm. There obviously is something to it.
The 6.5's have a sectional density that's better than a 308, and usually have some of the highest ballistic coefficients (rivaled only by the .338's and .50's). Considering it is a smaller diameter, you can load a lighter grain bullet and easily plink off some yotes up to 1,000 yards with this caliber and not do catastrophic damage to the game. But, if you load it up with a 140-150, you can easily take whitetail up to 850 yards. This is hands down one of the most versatile calibers out there. They aren't too expensive, factory ammo for the 6.5x284 Norma is right around $40-50 for 20. Reloading you can cut that in half. That's doable for any rifle owner.
I know Savage has a mean looking Norma in the 111 Long Range Hunter, comes with adjustable cheekpiece, muzzle brake (virtually no recoil with this), and you can pick them up for about $750. Uppers for the AR-15 are usually more than this anyway. Having an additional rifle is always a good option. Personal opinion, I don't like the AR's anyway.
Hope this helps some.