I have the A-Bolt II in the composite staLker 7mm magnum with boss. Proud Owner for $300 on clearance at Wal MArt (thanks Sam!!!) since 12/97. I can say that there is a noticeable reduction in recoil with the brake body over the CR body. Reduced recoil equals better shooting on part. I have so much confidence in the rifle - it's like a laser from the death star. Very well worth it in my opinion. The boss in general helps with accuracy - supposedly - since I've never shot it without the boss body on the gun.
As for noise - it is increased - by how much, I dont know. When at the range, I always wear ear protection. In the woods, the most I've shot is to empty the magazine - 4 rounds total. Ears rings for couple seconds - walk over to deer, ears clear before I get there. I or my friends don't notice anything different about the sound levels from my rifle over others in the woods. They do say that it has a somewhat distinctive sound. If you were shooting buffalo on the heard, I wouldn't do it - too much shooting without muffs - but for the one or two rounds I usually shoot, it's no problem for me. The other thing increased with the boss is the "muzzle blast", lol!!! When lying prone, the blast looks like the cloud from a rolling tank

- my buddies HOWL when we hunt groundhogs long range shooting. To each their own, however - I am a longtime boss owner. When I buy another bolt action rifle, it will be browning boss equipped. I just like it that much. I think a LOT of boss owners would / will say the same thing.
I've seen LAWDOG post the dangers of having muzzle brakes on rifles previously, so I think I know where he stands on the issue. I have no doubt that the boss is louder than a standard rifle - it is for sure. I would be curious as to his exact experiences with the browning boss system. It has only been out since about 1994.
For other information, I've also owned a T/C encore custom shop 30.06 with the T/C brake. It was not nearly as effective as the boss in my opinion.
Good Luck with your purchase - let me know if you need anything else.