Dang that’s a hard one to answer. Speaking only to a 6CM…
Purely to knock off any decibel I can? OG65. If my barrel was 19” or more? I’d lean OG-S. If the barrel was 18” or less I’d lean OG65. They’re really close.
As far as weight…personally they’re too close to call, I can’t really feel either one of them on the gun.
I’d likely make the decision based more on my rifle collection than the two cans. If I shot a ton of 223 and also owned a 6mm rifle, I’d go OG-S. If I owned 6.5mm rifles and 6mm, then OG65.
After today though, I’m glad I picked up the OG-S. That 6ARC barrel is 18.5” and at that powder charge weight I’d definitely rather save the inch.