I don't have a 6 ARC, but from my experience with the 6.5 Grendel, you can make a really good, reliable, accurate AR with that basic case. I don't think they really achieve the hyped level of performance but they do pretty well regardless. It could be a fun target rifle with a bit better long range hunting capability on lighter "big-game", but I'd go with 18" minimum barrel. I've had 2 barrels from low to mid quality spectrum, both will shoot 1/2MOA with their preferred bullets.
I'd be careful what you try to kill with it, the longer bullets in the small diameters might not get to reliable expansion velocities. My 6.5 grendel went through a white-tail like a dart. It didn't even flinch, i didn't even think I hit it until I saw it snort out a cloud of blood while I was lining up the second shot. it looked around, a bit, then just died. I'd imagine the 6mm could be even more prone to that based on my experience with .243.