I did a lot of research, and have come to the same conclusion. A brake will add around 10DB.
And though cool and interesting my funds will be better allotted to better range finder and spotting scope.
Measurements indicate that on a rifle a muzzle brake adds 5 to 10 dB to the normal noise level perceived by the shooter, increasing total noise levels up to 160 dB(A) +/- 3 dB.
Painful discomfort occurs at approximately 120 to 125 dB(A),
with some references claiming 133 dB(A) for the threshold of pain.
Active ear muffs
are available with electronic noise cancellation that can reduce direct path ear canal noise by approximately 17–33 dB, depending on the low, medium, or high frequency at which attenuation is measured.
Passive ear plugs
vary in their measured attenuation, ranging from 20 dB to 30 dB, depending on whether they are properly used.
Using both ear muffs (whether passive or active) and ear plugs simultaneously results in maximum protection, but the efficacy of such combined protection relative to preventing permanent ear damage is inconclusive, with evidence indicating that a combined noise reduction ratio (NRR) of only 36 dB (C-weighted) is the maximum possible using ear muffs and ear plugs simultaneously, equating to only a 36 - 7 = 29 dB(A) protection against a 160 dB(A) noise level.
Relative to a noise level of 160 dB(A), this means that even using ear muffs and ear plugs simultaneously cannot protect a shooter against permanent ear damage when using a muzzle brake, through leaving a shooter exposed to noise levels of approximately 131 dB(A) that is 11 dB above the point where permanent ear damage occurs.