I have built more than one upper with the Tromix 18" barrel and bolt combo. No issues at all and very accurate. That length is a good compromise offering nearly the fps/energy of the 20" and I like a shorter rifle for hunting. The mid-length gas system smoothes out the cycling compared to the carbine length gas length found on most 16" barrels. Aesthetically, I prefer a 12"-14" hand guard on my AR's and that length fits well on the 18" barrel in my opinion. The balance seemed a bit front heavy with the 20" barrel plus muzzle device as compared to the 18" Tromix too. If I could get dealer pricing from Tony I would use his barrels exclusively.
I have not tried the Gryphon barrels out yet. I am sure they are of great quality as well and bonus points for being Made in Michigan too! Maybe I can wrangle a demo barrel out of them so I can give them a good field trial. If someone wanted me to build an upper with a stainless barrel they would be my first call.
I have used both standard weight carbine buffer weights and the Spikes Tactical ST-T2 buffer with good results.
After two seasons and four deer shot with this setup I am now up to a total of 25 yards tracking. Dead Right There is the result I want in my hunting rig and this combination does the trick.