I always thought that a .243 AR would be neat but I have no desire to move into the AR-10 platform.I was gonna suggest building yourself something in 243. Back when I hunted, it was my go-to AR platform. Still a fun shooter, but in a 16" barrel, no telling how fast and flat it would be.
If I did it would most likely be the 6.5 Creedmoor that made me do it.