I've got a BAR in 300 winmag with the BOSS, and yes it is deafening. I've only ever shot it twice without hearing protection, different times, and both times I instantly regretted it and knew I had permanent hearing loss. With the brake, the kick is ridiculously little, it's less than a 12 gauge with buckshot by quite a bit. The brake makes it one of the most manageable 300 winmags out there, with likely just about one of the fastest recoveries. I can have a second shot off in maybe 2 seconds at 50 yards, and know it's a good shot.
I'm not even sure what you'd gain by having the BOSS-CR though, you'd gain alot of recoil that's for sure. And ya you wouldn't have as loud a gun, but I imagine it would still be loud enough that you would need hearing protection. I would not say that it's deafening even with ear muffs, loud yes, but there's no ringing or anything with ear muffs. Anyways it's all personal preference, my brother has a Savage 30-06 with a pad and then a limbsaver over the pad, and it kicks probably twice as hard as my BAR 300 winmag. To me, as irksome as it is to have to put on muffs in the middle of a hunt, the nonexistent recoil is worth it.