Craig,
Just talking about 8620 for a moment, since that is a popular choice among the custom singleshot rifle makers. 8620 has a normalized strength of about 90ksi and that data I referred to earlier states that casehardening will bring the core up to 135ksi. That says that 8620 is core hardening from the low teens in the RC scale up to the high 20's. If true, that would make for a great combination of core and surface hardness for a gun.