Think I read somewhere Estwings were @ HRC53 but can't say for sure.
As for GB, the 57 has been good enough for me (knifetests have done a trial showing the GB has substancial toughness), and lowering hardness is asking for more edge rolling, so it is ok as it is with me.
While an indicator, hardness is not the only factor.
Adequation between hardness and profile is the most important. Plus there are heat treatment details and forging that won't appear in hardeness while they add toughness.