The 6mm BR is an impressive cartridge. But it only shines when used in a bolt gun. The AR platform is not capable of running at those pressures. The Super Bolt only address one of the problems. It will take the head thrust but when it comes to Hoop strength the case is simply to big in diameter to push at the pressures of a bolt gun. I wouldn't push it past 35 to 40,000 PSI but that's my opinion.
If you compare apples to apples the 6X6.8 will and does run with the 6mm BR. The 6X6.8 will push a 58 grain Vmax 3600 FPS out of a 24" barrel. That is while being feed from a magazine. The data is out there to compare if you doubt what I say.
The last problem I see, is with the barrel from ARP "who made it" He is a vendor, not a manufacturer. If I am going to spend north of $400 for a barrel it better at least be a match grade barrel. I also would like to be able to order my barrel in the configuration that I want. Length is a big factor to get velocity. A 20" barrel is simply not long enough to get the top speed.