Cat the brake IS real noisy and obnoxious, just like it was supposed to be by order, but if you can get over the nasty blast, I think you will be surprised about how little recoil the rifle delivers. Not suggesting you want or need a brake, but more just for interest sake, if he will let you shoot it.
Max I think Jerry is close, but I have found with a brake installed on a 700P in 300 win , it shot more like a 700P in 223 than 308 maybe a slight bit more than 223 but not much. Long Range Canuck has a 300 I just built him and shoots 223 in a heavy Savage. PM him for his thoughts.
Brakes do tend to tame light rifles more noticeably than heavy 1s I believe, as the heavier rifles tend to deliver less recoil due to the weight. Also I have found that lighter calibers do not benefit as much as the bigger 1s do.