I have a Bushmaster dissipator barrel with a carbine length gas system. My barrel is really accurate. I have it setup on a A1 Colt upper with A1 handguards (which I had to modify internally slightly to fit around the gas block).
I would stay away from the rifle length gas system as Colt tried it with the Model 605 and it was very unreliable due to the limited dwell time.
I lightened this rifle for my girls to use shooting irons. The gas hole is around .110 and at that it is a very soft shooter.
The middy gas would be ideal if I were to do it over again.
I would go ADCO all the way. Even the tards on Arfcom are starting to figure out that CMMG is a big gamble.
I still have yet to get much more than 100 rounds through my adco custom cruiser, so I can’t give it a super combat rating. But Adco’s reputation is 100 time that of CMMG.