Having recently changed propellers on one of my planes, I have found the new one to be more noisy in the cockpit. This has sent me on a quest for more effective hearing protection. I had a David Clark H10.13XL ENC - it didn't do it. I borrowed a Bose A20, better. I went to the avionics shop for help.
The David Clark was not working properly, though was older technology anyway. I bought a David Clark One-X. Better, but still not as good as I wanted.
I have a David Clark K10 helicopter helmet (larger ear cups), so I tried that, not as good. I found that the cloth helmet within the hard shell did not hold the ear cups as firmly on my head, and the noise leaked in. Otherwise, it's a nice helmet though...
I contacted David Clark for advice. They told me that the H10.13XL would have superior noise attenuation to the One-X, it has bigger ear cups, with more foam. Yes, I had been there already, what else could I do. They recommended the H10.56, which is the headset version of the helicopter helmet I have. I had pieces of one of these, so was able to reassemble the H10.56. Instead of the regular foam which can be found in these headsets, I cut and fitted that super memory foam in the ear cups. That has produced the best result for noise attenuation.
I know that the OP is considering a helmet for protection, and that is excellent, but possibly it's noise attenuation will be a bit less than the same headset as a basic headset. 'Just my observations based upon very recent experience...