In the Becker sub-forum Toooj (Paul Tsujimoto) mentioned why they hardened to the amount that they did. I don't remember exactly but it was something like 5% extra hardness would lose about 30% toughness, that's why they don't make them harder than the RC57-59 they use.
Many things are a compromise and people like Shon Rowen and Paul Tsujimoto really know their stuff. They get the best of the steel with as close to the ideal hardness vs toughness as possible. I like my ESEE & Becker knives, partly because I trust in the work of those geniuses.
I can't find it, but I think Cliff Stamp had a chart showing how Rockwell hardness and temper of 1095 relates to Charpy impact test.