My deer rifle for years was the 6.5x47 Lapua. So my choice for my first AR-15 was 6.5 Grendel. I shoot the same bullets with some reduction in velocity, which is still more than adequate for deer & hog.
I am just finishing up my 2nd AR-15. This one is a wildcat, the 358Yeti. It is based on the .308 Win case shortened and expanded to 358.
It will launch 180gr bullets at 2,600 fps and 200gr at 2,400fps.
That is an interesting round, I need to look into it.